Forensic Failures: Ray Krone & Bite Mark Blunders

Forensic Failures: Ray Krone & Bite Mark Blunders

In 2002, Ray Krone became the 100th wrongfully imprisoned person to be exonerated by DNA analysis in the US, but only after spending ten years of his life detained in Arizona prisons, including a number of years on death row.

On the morning of 29th December 1991, the owner of the CBS Lounge in Phoenix, Arizona went to his bar to discover the door unlocked, the lights on, and the naked body of 36-year-old Kim Ancona on the floor of the men’s bathroom. The victim, who had worked in the bar as a waitress, had been brutally stabbed to death.

The subsequent examination of the scene was somewhat fruitless and, although saliva was recovered from Kim’s body, little other physical evidence could be found. The only piece of evidence investigators had to work with was a series of bite marks found on the victim’s breast and neck. As the investigation continued, police began interviewing those close to the victim in attempts to shed light on the events leading up to her death. It transpired that the victim had told a friend that Ray Krone, a regular customer at the bar, was to help her close up the bar the previous night. Investigators jumped at the possibility of a potential suspect.

During an interview with Krone, a detective noticed that he had a very distinctive deformity of his front teeth, no doubt causing a unique bite mark. This characteristic would later lead to the nickname of ‘the Snaggletooth Killer’. Krone was happy to oblige when asked to provide a Styrofoam impression of his teeth for comparison purposes.

However unfortunately for him, a forensic odontologist soon declared that the Styrofoam impression matched the bite marks found on the victim’s body.

Krone maintained his innocence, insisting that he was at home in bed at the time of the murder, a story corroborated by his roommate. Despite this, Ray Krone was arrested and charged with kidnapping, sexual assault and murder.

As the trial commenced, it was clear there was little evidence for the prosecution to present, so they focused their efforts on the bite mark comparison. They hired forensic odontologist Raymond Rawson to conduct the comparison between the bite marks on the victim’s body and the impression of Krone’s teeth. Using compelling video footage attempting to show the physical match between the two, Rawson informed the jury that the match was “100 per cent”, and that only Krone could have made those bite marks. The defence chose not to call upon their own court-appointed forensic odontologist.

Despite a lack of DNA analysis or eyewitness testimony linking Krone to the crime, and the bite mark comparison being the only physical evidence implicating him, Ray Krone was found guilty and sentenced to death.

Three years later Krone was awarded a re-trial due to the prosecution team concealing the persuasive video tape concerning the bite mark evidence until a day before the original trial, but once again he was found guilty. Despite the opportunity to rectify the conviction being wasted, trial judge James McDougall aired his uncertainty: “the court is left with a residual or lingering doubt about the clear identity of the killer. This is one of those cases that will haunt me for the rest of my life, wondering whether I have done the right thing”.

Forensic Odontology & Bite Mark Comparison

As DNA analysis was not carried out during this investigation, Krone’s conviction was almost entirely based on the ‘expert’ opinion that his teeth matched the bite marks on the victim’s body.

Dental identification is based on the theory that every individual’s dentition is unique, and thus bite marks made by a person will be distinguishable. In theory, this is true – we all have different combinations of jaw sizes, varying dental work and unique wear patterns to our teeth. Bite mark comparison may involve a variety of methods, including overlaying appropriately-sized photographs of teeth and bite marks and fitting together physical moulds.

At the time, there was little reason to doubt the testimony of the forensic odontologist hired by the prosecution. Raymond Rawson was a well-established expert who was certified by the American Board of Forensic Odontology, his findings in this case were supported by another expert, and the discipline of bite mark comparison had been practiced for almost 20 years. Furthermore, a 1984 study had provided “statistical evidence for the individuality of human dentition”. The expert witness testimony seemed perfectly reputable.

Well, that is until we look a little closer.

The seemingly convincing 1984 study was actually research conducted by Rawson himself, and has since been widely criticised as being a flawed study, largely because he used hand-traced dental impressions for his comparisons, a non-randomised subject selection process, and statistical tests not relevant to his type of data. Other experts had quite rightfully stated that the results of the study should absolutely not be used in a legal case.

A study conducted ten years previously comparing bite marks in wax and pig skin to the teeth of subjects stated that, although bite marks in wax were easily assessed, those made in pig skin were difficult to examine and the results unreliable. The research concluded that incorrect identification of bite marks on pig skin were made 24% of the time under laboratory conditions, and even as high as 91% of the time when based on photographs taken 24 hours after the bite marks were initially made. The study highlights the clear difficulties in subjective fields of work such as forensic odontology. Experts will often be required to examine bite marks that are hours or even days old, obscured by bruising and abrasions and typically not entirely representative of the biter’s teeth. At times it is challenging enough to merely identify an injury as a bite mark, let alone successfully compare it to a set of teeth.

Despite these apparent shortcomings, Ray Krone was to spend a decade of his life behind bars.


Fortunately for Krone, he had an undeterred family behind him maintaining his innocence and the means of hiring proficient legal help and in 2002, with the help of attorney Alan Simpson, he successfully appealed.

DNA analysis had become, by this point in time, a well-established technique frequently utilised in criminal investigations. Analysis of bodily fluids recovered from the crime scene a decade earlier soon proved not only Krone’s innocence, but also the identity of Kim Ancona’s real killer. Kenneth Phillips, a man with a long history of repeated violent sex offenses, was serving time in prison for the sexual assault of a 7-year-old girl, but at the time of Kim’s murder was living a mere 600 yards from the scene of the crime. Despite his close proximity to the bar, his deviant history and the fact that he was at the time of the murder on probation for the assault of a neighbouring woman, Phillips was never considered a suspect.

On 8th April 2002, Ray Krone left prison a free man, the 100th person to be exonerated by DNA evidence. He would certainly not be the last.

Krone now lives in Tennessee, where he has since dedicated his time to criminal justice reform and the campaign for the abolition of the death penalty.

“I would not trust the state to execute a person for committing a crime against another person. I know how the system works” – Ray Krone.



Innocence Project. Ray Krone. [online] Available:

New Scientist. Bite-mark evidence can leave false impression. [online] Available:

Rawson, R. D. et al. Statistical evidence for the individuality of the human dentision. J For Sci. 29(1984), pp245-253.

State v. Krone, 897 P.2d 621, 182 Ariz. 319 (Ariz. 06/22/1995)

Whittaker, D. Dome laboratory studies on the accuracy of bitemark identification. Int Dent J. 25(1975) pp. 166-171.

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Fragrance Forensics: Using Perfume to Catch the Culprit

Fragrance Forensics: Using Perfume to Catch the Culprit


Every day we apply chemicals to our bodies in the form of perfumes, colognes, deodorants and moisturisers, producing a concoction of pleasant scents that can be quite unique. It is well-known that perfumes and other fragrances can be potent and persistent, lingering on clothes and skin for hours if not days. Furthermore, these aromatic mixtures lend themselves to being easily transferred from one person to another through physical contact.

As the field of forensic science advances, investigators are looking for different ways in which they can identify suspects and connect individuals, and perfume may be an ideal target. What if the fragrance worn by an individual could be identified on a chemical level and used to link that person to a particular person or place? Simona Gherghel and fellow researchers at University College London have aimed to achieve this using analytical chemistry techniques.


Linalool (left) and limonene (right), common components in perfumes and colognes.

Different perfumes and colognes are composed of a variety of volatile organic compounds (VOCs), which provide the products with their powerful and characteristic scents. Compounds commonly detected in such products include linalool, limonene, coumarin, geraniol and eugenol, often in varying quantities and mixed with an assortment of other components. Once applied, these fragrances are absorbed by clothing and skin and can be readily transferred to fabrics and other surfaces.

Using gas chromatography-mass spectrometry (GC-MS), a well-established analytical technique frequently utilised in forensic enquiries, the team analysed fragrances in a number of scenarios to investigate the extent to which chemical components could be transferred between surfaces and what circumstances might affect this transfer.

The research focused on a number of factors relevant to the use of fragrances as a potential form of trace evidence in forensic enquiries, specifically the method of transfer and the time between application of the fragrance and contact with another surface. Experiments involved contact between swatches of fragranced and fragrance-free fabrics, examining transfer of compounds when the fabrics were in contact with no friction, and forcefully rubbed together over periods of time ranging from 1 minute to 60 minutes. After controlled contact, swabs were collected from the fabrics and subjected to GC-MS analysis. Unsurprisingly, extended contact time led to an increase in transferred components. This may have the potential to indicate how long a victim and offender were in physical contact, whether it be fleetingly or for a prolonged period of time, the latter being more likely in the case of an assault.

This research also investigated the effects of time passed between application of a fragrance product and contact between two surfaces on the transfer and persistence of VOCs. Contact between a fragranced piece of fabric and a fragrance-free swatch was investigated at a number of time points ranging from contact occurring 5 minutes after fragrance use and to 7 days after use. As was expected, the number of chemical compounds transferred between the fabric swatches decreased with time, with larger-sized, less volatile molecules persisting for longer. When only 5 minutes had passed before contact occurred, an average of 24 volatile components were transferred from the perfumed fabric. However after 6 hours only 12 components were detected, and this decreased to only 6 components after 7 days. Although this shows that certain transferred chemical compounds can persist for days, there is a discernible decrease in their presence which ultimately makes the sample less detectable and less unique, as a smaller mixture of chemicals are available for identification and comparison.

Although this is the first published work demonstrating the transfer of fragrance between garments in a forensic setting, the possibility of identifying perfumes based on their chemical composition for forensic purposes has been previously examined by experts at Staffordshire University in the UK. Led by PhD student Alison Davidson, the team has been compiling chemical profiles of popular perfumes and colognes with the hope of distinguishing between brands of difference fragrances and ultimately using this information to aid criminal investigations.

The ability to identify perfumes and establish physical contact between two individuals based on VOCs could be of particular use in the investigation of sexual assaults and other violent crimes in which the victim and offender were in close contact. For instance, the contact between a victim’s perfumed clothing and the clothing of the offender could cause the transfer of volatile organic compounds to the offender’s clothing (or vice versa). Later analysis of a suspect’s clothing may then result in the identification of chemical compounds originating from the victim’s perfume, indicating physical contact and thus potentially supporting an accusation.

Although the research conducted has supported the possibility of utilising transferred VOCs in perfume and possible affecting factors to aid legal investigations, it is vital to consider that a greater range of variables must be taken into account if such analyses were to be utilised in real life scenarios. The degree of activity by the victim and offender and the time passed between the offense and forensic analysis must be considered, as should how unique the mixture of chemical components detected really is. Furthermore, if the transfer of perfume between fabrics can occur so easily, there is a distinct possibility that such a transfer could occur in entirely innocent circumstances, highlighting the importance of such analysis only being utilised alongside alternative sources of evidence.

The concept of studying the chemical composition of perfumes and fragrances to aid legal investigations is very much in its infancy, but with further research this technique may have the potential to offer investigators an additional tool to sniff out suspects.



S. Gherghel, et al., Analysis of transferred fragrance and its forensic implications, Sci. Justice (2016), 10.1016/j.scijus.2016.08.004


Interview with Biological & Forensic Anthropologist Dr Geraldine Fahy

Geraldine Fahy

What is your current job role and what does this involve?

I am a lecturer in Biological/Forensic Anthropology in the Skeletal Biology Research Centre, University of Kent. During term-time I teach all aspects of Human Evolution from early fossil hominins, hunter-gatherer societies, to methodologies used to reconstruct the last common ancestor (LCA). I also convene a forensic anthropology module where I teach forensic taphonomy, excavation and recovery, disaster victim identification and biometric identification. We are in the process of developing our MSc Forensic Osteology and Field Recovery Methods which will run from Sept. 2017 which is very exciting!

What initially attracted you to this field of work?

I wanted to become a forensic anthropologist from the first time I read Kathy Reich’s debut novel, Deja Dead. Of course, fiction is fiction however by the time I started researching the topic and where I could study forensics, I loved the topic for itself, for the science and so continued. I have turned more towards analytical chemistry techniques and human evolution in recent years; however, my interest in forensics continues, and my education and employment background remains relevant, as most forensic science disciplines, including forensic anthropology, have solid foundations in science, with the ‘forensic’ aspect being related to chain-of-custody maintenance and courtroom presentation.

Can you tell us about the research you are currently involved in at the University of Kent?

I conduct research into dietary ecology and subsistence patterns of past populations using stable isotope analysis. I have previously conducted such research on a population of wild Western chimpanzees, as correlates for the LCA; however, my current research focuses on medieval dietary reconstruction from East and West Europe. I am also currently involved in a project looking at the effects of bone turnover rates on stable isotope values and am currently investigating potential stable isotope methodologies that may have future use in forensic identification.

Has your work led you to be involved in any legal investigations? If so, what did this involve?

I worked as a forensic anthropology intern at the Netherlands Forensic Institute where I looked at decomposition of muscle tissue following submersion in water for my MSc thesis. Following this I worked as a forensic anthropology intern for the UN Mission in Kosovo in 2007 where I assisted in the identification and repatriation of victims of the Yugoslavian conflict. Subsequently I worked as an Associate Forensic Expert for the UN International Independent Investigation Commission in Lebanon which involved evidence collection and cataloging in the investigation of the assassination of former Lebanese Prime Minister Rafik Hariri and others.

Do you have any words of advice for students wishing to pursue a career in forensic anthropology?

Do your research but don’t be disheartened if you end up doing a different degree initially; as long as it’s not totally removed (e.g. doing a business degree when you then want to work in science) it is possible to get where you want to go without a straight path. I would advise doing as many unpaid internships as possible, this is where you gain valuable experience and make contacts for the future. Importantly realise that what you want can change as the years go by and this is fine….you may start out wanting to work constantly in the field, but then realise this is not viable for you and end up in a lab or a classroom, just go with whatever feels right for you.


Interview with Forensic Anthropologist Dr Anna Williams

hud pic

What is your current job role and what does this involve?

I am Principal Enterprise Fellow (equivalent to Reader or Associate Professor) in Forensic Anthropology at the University of Huddersfield. My time is divided between teaching undergraduate and postgraduate students, supervising MSc and PhD students, and doing research and forensic casework. I teach on the BSc/MSci Forensic and Analytical Sciences, and the MSc in Forensic Anthropology and the MSc in Risk, Disaster and Environmental Management. Part of my role is also to engage with the public and communicate our research to lay people, including school children, interested adults and other scientists. I regularly present at academic conferences, local interest groups, Science Festivals and public events. This year, I am presenting at the Royal Society Summer Science Exhibition. I have also been featured in several TV science documentaries, and regularly consult for TV shows like Bones, Rosewood and Silent Witness. I also write a blog about my adventures in forensic anthropology.

What initially attracted you to this field of work?

I did a mixture of sciences and humanities at A Level and could never decide which I liked best, so I chose Archaeology and Anthropology as my first degree. There, I was fascinated by what you could tell about individuals by their skeletal remains, for example about hominid evolution. Then I discovered the burgeoning science of Forensic Anthropology, on a short course at Bradford University, and that was it, I was hooked! I love how you can glean all sorts of information from the smallest pieces of evidence. I have always loved logic problems, and forensic anthropology offers the most exciting puzzles. The fact that it is often confronting, challenging and disturbing, and could help to bring criminals to justice, just serves to add to its appeal for me.

Can you tell us about the research you are currently involved in at the University of Huddersfield?

I specialise in decomposition and taphonomy (the study of how bodies decay in different environments). To do this, I use an outdoor decomposition laboratory. I lead a research group currently doing research into the gases given off by decomposing cadavers (we use pigs that have died of natural causes), and comparing that to the efficiency of police dogs that are specially trained to find dead bodies. We’re also looking at how skin colour changes in surface or water environments, and trying to find ways to improve our estimation of post-mortem interval and post-mortem submersion interval. Other research is focussed on the taphonomic changes that occur to bone and teeth in hot, arid environments. I am also running a citizen science project in order to improve age estimation of unknown individuals from dental eruption. There is a webpage and online questionnaire for anyone who would like to help us build a large, modern set of tooth eruption data to see if dental eruption ages are changing.

Aside from research, are you often involved in police casework, and what does this typically involve?

Sometimes I am asked by the police to attend crime scenes or mortuaries to undertake forensic examination of decomposed or skeletonised remains. They can be either the victims of crime, or the remains of people who have gone missing. I will determine whether they are human or animal, and if they are human, I will estimate the age at death, sex, stature and ancestry of the individual(s), and try to say something about their lifestyle, disease, injury and how they died. I work in conjunction with forensic archaeologists and odontologists, as well as pathologists, to reach an identification. I also do consultancy for forensic science providers and, on occasion, a mass disaster company that helps to ‘clean up’ after disaster and repatriate the victims. I am involved in disaster victim identification and the Emergency Operations Centre.

The existence of so-called ‘body farms’ has sparked great interest in the media. Are there plans to establish such a facility in the UK? What are the primary challenges associated with this?

I believe that Human Taphonomy Facilities, or ‘Body Farms’ as they have become colloquially known, are vital for the advancement of forensic science. We owe all that we know already about human decomposition to the Forensic Anthropology Center at the University of Tennessee, and there is so much more to learn. We need to know how human conditions like diabetes, cancer, smoking and drug use affect our decomposition, which is something we cannot learn from experimenting with dead pigs. Unfortunately, a lot of the data generated by the ‘Body Farms’ in the USA and Australia are not directly relevant to forensic cases in the UK or Europe, because of the different climate, insects and scavengers. The UK is falling behind the USA and Australia by not having one of these outdoor laboratories where vital decomposition research can be done on donated cadavers. There was an attempt to establish a Body Farm in the UK in 2011, but this failed for a variety of financial and political reasons. I think the main obstacles to getting one set up in the UK are lack of funding, public awareness and rivalry between academic institutions. I hope that, in the near future, we will be able to create a facility where researchers, academics and practitioners will be able to work together to improve methods of search and recovery, post-mortem interval estimation and identification of human remains.

Do you have any words of advice for students wishing to pursue a career in forensic anthropology?

Forensic anthropology is a very competitive field, and there aren’t many jobs out there, so you need to be dedicated and determined. It can also be hard work and distressing, so decide carefully whether you want to pursue a career in it. The best way to make yourself stand out from the crowd of other applicants to jobs is to have experience, so try to get as much hands-on experience as you can. This doesn’t have to be forensic (although, of course, that would be preferable), but can be in archaeological units or museums or hospitals (or even zoos), somewhere where you can deal with human (or animal) bodies.

Images from Research

These pictures show the progression of decomposition in a small (10kg) pig. The first picture shows the pig in the fresh stage, when post-mortem interval was less than 24 hours. The second picture shows the pig in the active decay stage, 25 days later. The brown froth is decomposition fluid that has been agitated by the movement of maggots. The body was bloated with decomposition gases, but has now collapsed, and the intestines are escaping. The skin has desiccated, but the hair is still intact. The skin has darkened and become leathery in texture. The bones are becoming detached from the body.


Surface pig 1, day 0


Surface pig 1, day 25



Twitter: @Bonegella

Also, you can follow #scentofdeath and #teamtaphonomy

Introducing the Controversial Psychoactive Substances Act

Introducing the Controversial Psychoactive Substances Act

As of this week the Psychoactive Substances Act came into effect in the UK, a long-awaited and much-disputed piece of legislation that will attempt to transform the existing drug marketplace. The act will make it an offence to supply any substance that can produce a psychoactive effect (of course with the exception of the likes of alcohol and caffeine), aiming to specifically target new psychoactive substances (NPS) or ‘legal highs’, which have thus far evaded the Misuse of Drugs Act.

But just what are New Psychoactive Substances, and why has it been so difficult to enforce laws against their supply and use?


NPS are synthetic chemical substances created to mimic the effects of existing illegal substances, such as cannabis or ecstasy. These drugs are often designed in such a way that they are sufficiently chemically similar to an illicit drug to cause the desired psychoactive effects, but adequately different to bypass the existing legislation.  The legislation currently controlling illicit substances in the UK is specific in the substances under regulation, meaning any slight changes to the chemical structure of an illicit drug can technically render the drug uncontrolled and legal to supply or use.

New psychoactive substances are typically sold as powders, pills or smoking mixtures (somewhat resembling cannabis). You may have heard these drugs referred to as “legal highs”, rather inaccurately indicating they are legal and even safe to use. But a brief internet search will pull up an array of news pieces highlighting unexpected illnesses and deaths brought on by the use of these drugs. The primary danger surrounding the use of new psychoactive substances is the lack of research involving these substances, exacerbated by the ever-changing and difficult-to-monitor composition of the drugs. In addition to this, as NPS are specifically sold as being unsuitable for human consumption, thus avoiding certain regulations, the user cannot be confident in exactly what they are buying. Although many legal highs do offer a list of ingredients on the packaging, the highly unregulated nature of this market casts doubt on the accuracy of such information. Forensic analysis of NPSs has shown that they may contain unexpected constituents and even quantities of illicit drugs.

The NPS market has boomed in recent years, with new drugs hitting the streets faster than scientists can even identify them. They have thus far been widely available online and in head shops (establishments openly selling paraphernalia for the use of cannabis and other drugs), typically advertised as bath salts or plant food. Unfortunately the ever-changing variety of ‘legal highs’ available has presented forensic scientists with a particular challenge. The analysis of more typical drugs is relatively straightforward, with the analyst armed with well-trialled presumptive tests, analytical methods and libraries for comparison. However as new psychoactive substances are developed with modified chemical structures, they may not react with presumptive tests and library matching may prove useless without a comparison.

The premise of the act has come under great scrutiny, with opponents asserting the Act will blindly ban harmless substances (not true) or that it will be utterly unenforceable (somewhat true). A similar piece of legislation has been instigated in the Republic of Ireland, but with little success, as highlighted by the extremely low number of successful prosecutions under the law. In fact, the implementation of this legislation in Ireland was actually followed by an increase in NPS use amongst teenagers from 16% to 22%. That is not to say the legislation was the cause of this increase, but it is an interesting point nonetheless.

Despite the criticism and uncertainty, the Psychoactive Substances Act will attempt to curb the supply of psychoactive substances and protect potential users of these drugs. Although it will not be an offense to possess new psychoactive substances for personal use, it will be a criminal act to supply such substances. It will be inconceivable to halt the online sale of psychoactive substances, but it will be possible to prevent head shops, of which there are hundreds around the UK, from blatantly advertising and selling these drugs. Although the Psychoactive Substances Act promises to be a difficult piece of legislation to enforce, if at the very least it prevents new psychoactive substances from being freely advertised as a normal and ‘safe’ alternative to drugs, a great improvement will be made. But only time will tell if this new piece of legislation will really reduce the use of these no longer legal highs.



Home Office.Trade in so-called ‘legal highs’ now illegal. [online] Available:

New Psychoactive Substances Act 2016 [online] Available:

Investigating Secondary DNA Transfer

Investigating Secondary DNA Transfer

DNA evidence has largely been viewed as the ‘gold standard’ of forensic science, offering a seemingly solid means of linking individuals to crime scenes and, in more recent years, exonerating those wrongfully convicted. Whereas successful DNA analysis previously required a visible biological contribution, for instance a drop of blood, new advances in DNA technology have allowed for profiles to be produced from just a few dozen cells (you may have heard the term ‘Touch DNA’ be used to describe this). But as DNA technology has advanced, the improved sensitivity of DNA analysis techniques has become something of a double-edged sword, with concerns being raised over DNA analysis being too sensitive.

Imagine a scenario. A man and a woman are having an innocuous conversation. Some physical contact happens, perhaps the touching of hands or the brush of a cheek. The woman later experiences a sexual assault and an investigation ensues, an investigation in which DNA evidence is likely to play a pivotal role. During a sexual assault investigation, it is likely that swabs may be taken of a suspect’s clothing and genitals, specifically aiming to detect any of the victim’s DNA. This may particularly be the case if no semen has been detected, necessitating any other means of establishing whether or not sexual contact may have occurred.

But is it possible for a person’s DNA to be inadvertently transferred to the clothing or body of another person through innocent contact, only to later wrongfully incriminate that person? Research recently published in Science & Justice aimed to provide some insight into this question.

The aim of the study was to determine the frequency and amount of DNA transferred from a female to a male’s underwear and genitals following a non-intimate social contact situation. Using a staged scenario in which a male and female are interacting, the male participant was asked to touch the female’s face for 2 minutes and then hold her hands for 3 minutes whilst maintaining a conversation. This exchange provided the opportunity for the direct transfer of DNA from female to male. Following this exchange, the male participant went to the bathroom to simulate urination, offering the opportunity for secondary transfer of the female’s DNA to the male’s underwear and genitals. Other trials also introduced a 6-hour delay between the social contact and bathroom visit. Swabs were then taken of the man’s underwear and penis. In separate experimental trials, the same swabs were taken from male participants immediately following unprotected sexual intercourse to act as a comparison.

Following SGM Plus DNA profiling (routine at the time of the research), female DNA was found on the waistband of the underwear on only 5 occasions out of 30, on the penis in 4 out of 30 samples, and just once on the front panel of the underwear. In no other instances was female DNA detected. Unsurprisingly, this was even lower in trials implementing a 6-hour delay. In comparison to swabs taken from a male following sexual intercourse, transferred female DNA was detected in all samples and in larger amounts. So although the research demonstrated the possibility of the transfer of the female’s DNA to the male’s underwear and genitals (obviously somewhat incriminating if this occurred during a sexual assault investigation), the frequency and level of occurrence was much lower than if sexual intercourse had actually occurred.

The concept of secondary DNA transfer is not novel, and it has been known for some time that it is possible for DNA to be transferred through everyday contact. In fact the very idea of secondary DNA transfer was first described in literature almost two decades ago (Oorschot & Jones, 1997). The aforementioned research follows previous studies conducted investigating similar scenarios but reaching somewhat different conclusions.

Research published last year by the University of Indianapolis conducted their own DNA transfer study in which participants were asked to shake hands for two minutes before one of the participants handled a knife. The study aimed to determine whether this social interaction and handling of the object was sufficient to allow DNA from one individual to be passed to the knife via secondary transfer, without that person coming into any direct contact with the knife itself. Subsequent analysis of the knives showed that in 85% of cases DNA detected on the knife belonged to the participant who had not handled the object, and in one-fifth of the samples they were even the main or only contributor of DNA found on the weapon. This study essentially implies it is possible for someone to be linked to a crime scene via secondary transfer of their DNA to a murder weapon or victim, for instance.

Conversely, research published back in 1997 also conducted similar research, but this time not supporting the idea that secondary DNA transfer can provide misleading results (Ladd et al, 1997). Participants were instructed to shake hands for varying lengths of time before handling an everyday object, such as a coffee mug. The research concluded that a complete DNA profile of the secondary participant (who had not directly handled the object) was never detected. So although various studies have been carried out, although using different experimental conditions, results are to an extent contradictory.

These studies discussed have obvious limitations. The scenarios staged are far from realistic – the average person does not shake someone’s hand for two minutes before handling an incriminating object, which is then immediately swabbed for DNA by investigators. Nor does the research take into account factors that might affect DNA transfer and persistence.

It is worth noting that these concerns are not confined to the research lab. In 2010, former cab driver David Butler found himself imprisoned, accused of murdering 46-year-old Anne Marie Foy. The evidence against him? His DNA allegedly found under the fingernails of the victim. Butler had previously offered up a DNA sample years before during the investigation of a burglary and, although the DNA profile obtained from the victim’s body was merely a poor quality partial match, this was seemingly sufficient to land Butler in prison on remand for nearly eight months. However the DNA evidence was later called into question when it was suggested that Butler, who had a skin condition causing him to shed more skin cells than the average person, could easily have transferred his own DNA to a person or money which was then transferred to the victim via secondary transfer.

Cases such as this highlight the need for further investigation. Although recent research has provided a good starting point for investigating secondary DNA transfer through non-intimate contact, as DNA analysis techniques improve and achieve greater sensitivity, there will be an increased need to extend research. Further studies examining new DNA profiling techniques, different scenarios and the effects of possible affecting factors will be necessary in ensuring secondary DNA transfer in situations of everyday social contact will not be mistakenly interpreted in a criminal investigation.



Van Oorschot, R. A. Jones, M. K. DNA Fingerprints from Fingerprints. Nature. 387(1997), 767.

BBC News. DNA test jailed innocent man for murder. [online] Available:

Cale, C. M. et al. Could Secondary DNA Transfer Falsely Place Someone at the Scene of a Crime? J Forensic Sci. 61(2016) pp. 196-203.

Jones, S. et al. DNA transfer through nonintimate social contact. Sci Justice. 56(2016), pp. 90-95.

Forensic Failures: Three Men, Three Hairs, Three Wrongful Convictions

Forensic Failures: Three Men, Three Hairs, Three Wrongful Convictions

In the summer of 1978, 63-year-old taxi driver John McCormick was robbed and shot on his own doorstep in his Washington, D.C home. His wife, roused from sleep by the cries of her husband pleading for his life, ran to his aid to briefly glimpse the gunman, a man with a stocking mask shielding his face. McCormick died as a result of the attack, shot by a .32 calibre handgun. A police officer and his dog later found the stocking mask nearby, and from this a number of hairs were recovered.


Santae Tribble (Source: The Innocence Project)

Suspicion soon fell on 17-year-old Santae Tribble, implicated by an informant, Bobby Jean Phillips, who claimed Tribble had recently sold a .32 calibre handgun to her roommate. A weapon that, incidentally, was never successfully linked to the gun used to kill McCormick. Tribble was pulled in for questioning. Hairs recovered from the stocking used by the killer were compared to samples collected from the suspect and, according to an FBI analyst, “matched in all microscopic characteristics”. At trial, the prosecution went on to declare that there was perhaps a “one chance in ten million” that the hair belonged to someone else. Seemingly compelling “statistics” and apparently sufficient in helping the jury reach a verdict. Despite having testified that he was in Maryland at the time of the attack, an alibi supported by half a dozen witnesses, in January 1980 Santae Tribble was found guilty of murder and sentenced to 20 years to life in prison.

Meanwhile, as Tribble was adjusting to prison life, another man’s world was about to be turned upside down thanks to a single hair. In February 1981, a 27-year-old woman was bound, raped and robbed in her apartment, briefly glimpsing her attacker in the dim light. The distraught victim helped police construct a composite sketch of her attacker; a young, cleanly shaven African American man. Unfortunately for 18-year-old Kirk Odom in the following weeks, a passing police officer decided that Odom resembled the composite sketch, passing on his suspicions to the detective leading the case. As a result of this Odom was presented to the victim as part of a somewhat dubiously organised line-up, with Odom standing on a box in order to match the height of the other men in the line-up, who were actually police officers. The victim identified Odom as her attacker.


Kirk Odom (Source: The Innocence Project)

During the trial, FBI Agent Myron Scholberg testified that the “Negroid hair” found on the victim’s nightgown was microscopically similar to a hair sample taken from Odom, “meaning the samples were indistinguishable”. He declared this to be “a very rare phenomenon”, and in the thousands of occurrences in which he had compared hair samples, on only eight or ten occasions had he failed to distinguish the hairs of two different people. Understandably, this implied a very substantial likelihood that the hair did in fact belong to Odom, and after only a few hours deliberating he was found guilty and sentenced to 20 to 66 years in prison.

In June that same year, a worryingly similar scenario ensued after 21-year-old student Catherine Schilling was found raped and murdered in Rock Creek Park, Washington. She was discovered naked and shot five times in the head. A somewhat questionable police informant, Gerald Mack Smith, relayed to police that he had been drinking in the park with a man who had admitted to killing the woman after attempting to rob her. That man was allegedly Donald Eugene Gates. It is worth noting that, not only was Smith paid by police for his information, but at the time he had two prior felony convictions and had recently been indicted for a third felony, which was conveniently dismissed after he aided the police in incriminating Gates. This information was not relayed to the defence team.

Donald Gates - Washington Post

Donald Gates (Source: The Washington Post)

So Donald Gates, aged 30 at the time, was arrested and charged with murder, not only based on the testimony of Gerald Smith, but also largely on the comparison of hair samples. FBI forensic analyst Michael Malone testified in this case, establishing that hairs recovered from the scene were “microscopically indistinguishable” from a hair sample taken from Gates. The expert witness claimed that in his many years of hair comparison work, there were perhaps two in ten thousand cases where hairs from two people could not be distinguished. Once again, seemingly convincing statistics to a lay jury. In September 1982, Gates was found guilty and sentenced to 20 years to life in prison.

Forensic Hair analysis

What do these three cases have in common? All men were wrongfully convicted for crimes they did not commit. And all convictions were largely based on flawed expert witness testimony relating to hair analysis.

The potential evidential value of human hair stems from its prevalence at crime scenes and the ease with which it can be imperceptibly transferred. It is fairly resilient and can persist at a crime scene for many years after the incident took place, all-in-all making hair a potentially vital piece of evidence well worthy of examination.

What does this examination involve? Forensic hair analysis is a type of ‘comparison analysis’ – that is an examination that is typically based on individual or class characteristics rather than incorporating numerical analyses. It generally involves the study of microscopic characteristics relating to whether the hair is human or animal, the colour, length, diameter, likely racial group, area of bodily origin, phase of growth, and so on.

Hair 2 - Wikimedia

Microscope image of hair sample

The examination may include an even closer scrutiny of patterns and intricacies along the shaft of the hair. The human hair can be described as being composed of three distinct regions: the medulla, the cortex and the cuticle. The medulla refers to the inner core of the shaft, the cortex as the surrounding material, and the cuticle the outermost protective layer. The cuticle is composed of a scale-like complexion, which can be particularly beneficial in distinguishing between animal hairs and human hairs. Cuticle characteristics will be noted in the comparison of hair samples, particularly the thickness of the cuticle, the colour, and the general shape of the “scales”. The cortex is the portion of the hair containing pigment granules which give hair its colour, obviously vital in the comparison of different samples. These pigment granules vary between racial groups, thus are pivotal in establishing whether a hair is likely Caucasian or Negroid in origin, for instance. The medulla in the centre of the hair shaft will also be scrutinised to determine whether the core is continuous, interrupted, fragmentary or absent.

This is a limited list of the features focussed on during forensic hair analysis. In reality there is a myriad of other features, both natural such as those above and artificial such as dyeing and damage, that can be used in studying the similarities and differences between hair samples. So it would seem there is an abundance of information with which to reach a conclusion. However the problem lies in that these are all class characteristics whose description is based on the individual analyst’s subjective observations.

Obviously the ideal situation would involve some form of statistical analysis to determine the reliability of comparisons, but the vast number of variable factors in hair comparison makes statistical analysis tremendously complex if not impossible. This in itself does not render such analyses worthless in criminal proceedings, provided accurate testimony is given and caveats made clear. In the aforementioned cases, and potentially others, expert witness testimony strongly implied that exact matches between hair samples had been made, and in some instances fictitious statistics were even expressed to the jury. When such evidence is presented by a seemingly distinguished scientist who may be an expert in their field, naturally members of a lay jury with little or no knowledge of the topic are unlikely to challenge this evidence. The FBI’s own guidelines on forensic hair analysis conclude that “the science of microscopic hair examination can never result in an identification” but can “provide a strong basis for an association”, but unfortunately this ethos was not always carried into the courtroom.

Collectively, Tribble, Odom and Gates served nearly 80 years in prison. All three men were eventually released and exonerated by DNA testing and the actual perpetrators identified. However by the time this was achieved, perpetrators had passed away or were able to evade conviction due to expiration of the statute of limitations. The wrongfully convicted men were awarded millions of dollars in compensation, but hardly a prize worthy of losing so many years.

As a result of these incidents, and numerous others, ongoing investigations are aiming to identify further miscarriages of justice in the United States, initially largely powered by the Innocence Project, a non-profit organisation which aims to exonerate wrongly convicted people through DNA testing. Furthermore, efforts are underway to focus on how forensic science standards can be strengthened to avoid future errors, particularly in relation to forensic ‘comparison analyses’.



Federal Bureau of Investigation. Forensic hair comparison: background information for interpretation. [online] Available:

Innocence Project. Donald Eugene Gates. [online] Available:

National Registry of Exonerations. Kirk Odom. [online] Available:

Taupin, J. M. Forensic hair morphology comparison – a dying art or junk science? Sci & Justice. 44 (2004), pp. 95-100.

The Washington Post. Santae Tribble cleared in 1978 murder based on DNA hair test. [online] Available: