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


Studying Steps: Forensic Gait Analysis

Studying Steps: Forensic Gait Analysis

In July 2000, forensic history was made when a jewellery thief was prosecuted with the help of forensic evidence. But this was not through DNA analysis or fingerprint comparison, as one might expect, but by studying the perpetrator’s gait. That is, how the individual moved. When podiatrist Haydn Kelly was called upon to offer his professional opinion in the case of a suspected jewellery thief, the expert was able to identify the suspect from video footage through nothing but the study of the individual’s walking mechanics, ultimately declaring that he believed the perpetrator captured in the video was the same as the person under suspicion.

Forensic gait analysis refers to the identification of an individual based on the characteristic features of the way in which they move. This sub-section of forensic podiatry (the study of evidence relating to the human foot) is based on the theory that people have unique movement characteristics as they move their body and limbs.

These characteristics may be subtle, for instance the angle of the feet throughout movement, or they may be fairly distinguishing, such as the condition of genu varum (bow-leggedness), which led to burglar John Rigg’s identification and subsequent conviction in 2008.

An individual’s gait can be affected by a range of factors, including sex, weight, height, age, but also taking into account external factors such as terrain, clothing and if they are carrying anything. Gait is a behavioural biometric and thus is subject to change based on a person’s emotional state or whether they are, for instance, in a rush to get somewhere quickly or under the influence of drugs or alcohol. It is worth nothing that the term ‘gait’ is not synonymous with walking, but refers to locomotion in general, whether that be walking, running, crawling, and so on. Furthermore, a person’s gait does not only relate to the movement of their feet and legs, as one might expect, but can also encompass their upper body movements, namely their arms and torso.

The repetitive gait cycle is said to be divided into two distinct phases; the stance phase, during which the lower limbs are providing support for the body by being in contact with the ground, and the swing phase, at which point the foot is no longer in contact with the ground. It is the spatial and temporal measurements throughout these phases that can be of great use to the gait analysis expert.


The Forensic Analysis of Gait

With the proliferation of closed circuit television (CCTV) cameras worldwide, it is becoming increasingly commonplace that a perpetrator is caught on camera in the act of committing of a crime. However this footage may not always be beneficial in identifying the subject based on their face. Perhaps the perpetrator has taken steps to conceal his or her identity or, more likely, the footage is simply not good enough for identification. A vast array of factors can affect the usefulness of CCTV footage, including camera quality, distance, lighting, environmental conditions and the angle of the recording. Thus all investigators may be left with is the blurry figure of their perpetrator. Not especially useful for identification purposes one might think.

So how can an expert use the study of a person’s gait to identify an individual? Well, it’s a little more complex than watching someone walk and deciding they look the same as a perpetrator captured on CCTV.

Identification in gait analysis is a comparative process – the footage of a perpetrator is compared with footage of a suspect walking and the similarities and differences are assessed. This analysis may be qualitative, involving the visual evaluation of movement by an expert, or quantitative, a far more complex process involving the collection, interpretation and comparison of numerical data relating to the movements.

The analysis of video evidence of a suspect typically involves the painstaking inspection of each frame of the video, identifying the slightest characteristic movement of the legs, arms, shoulders and head. A vast array of parameters will be studied throughout the analysis, including the length of steps and stride, speed and rhythm of walking, and finer points such as the angles of feet and hips as the individual moves. The analysis will additionally extend to any possible affecting factors, such as whether the perpetrator was carrying something substantial in the footage, such as a hefty bag of stolen goods, and how this might alter his or her gait. Any affecting factors such as these must be taken into account when recording footage of a suspect for comparison purposes. Footage of a person walking in light clothing and empty-handed is hardly a suitable comparison for a video of the perpetrator in a bulky coat and carrying a heavy rucksack.


Although gait analysis is a relatively new approach in forensic science, the study of a person’s unique patterns of movement is far from novel. Gait analysis has been utilised in a medical setting for decades, focusing on the study of abnormalities in a person’s gait for the purpose of medical research and treatment. Similarly, gait has been studied in sports to aid athletes in perfecting their running technique, for instance. This history has allowed for the development of well-established procedures in studying and comparing the movement of individuals.

Technological Advances

Unsurprisingly, forensic gait analysis is not without its caveats, and experts in the field hasten to concede that it is not an indisputable field of study. Whereas DNA analysis and fingerprint comparison can, to an extent, provide clear evidence as to a connection, gait analysis is best utilised as a guideline as to the possibility of an identification being made. Although gait analysis is well-established in a clinical setting, the evidence available in a forensic setting is typically of relatively poor quality in comparison to that available in medical studies, thus footage may not actually be suitable for gait analysis in the first place.

The analysis of gait conducted by a human expert can obviously introduce the potential for human error and subjectivity, even calling the conclusions reached by experts into question, especially considering the lack of quality control in this field of study. A 2013 study concluded that people who were experienced in visual gait analysis were only able to consistently identify individuals based on their gait 71% of the time (Birch et al, 2013), indicating the scope for error.

Despite the obvious downfalls of gait analysis conducted by humans, the possibilities of gait as a form of biometric identification has sparked a great deal of research into the development of automatic gait recognition technology. Computer-based systems have already been developed that examine video frames and separate the silhouette of the individual in question from the background, then recording that individual’s movement. This, and similar systems, in theory allows for the detection and tracking of humans by using computer systems to store an individual’s ‘gait signature’ and later identify that person when they are next caught on camera. The development and use of automated gait recognition systems would reduce the scope for human error, greatly increase the speed of analysis, and allow for real-time identification based on gait. If sufficiently developed, such technology could even form the basis of new security systems, only allowing access to the unique gait of particular individuals, much like retinal or fingerprint scanners. Though gait analysis technology may still be in its infancy, the scope of potential applications is great.


BBC News. How can you identify a criminal by the way they walk? [online] Available:

Birch, I et al. Terminology and forensic gait analysis. Sci Justice. 2015(55), pp. 279-284.

Birch, I et al. The development of a tool for assessing the quality of closed circuit camera footage for use in forensic gait analysis. J For Legal Med. 2013(20), pp. 915-917.

Birch, I et al. The identification of individuals by observational gait analysis using closed circuit television footage. Sci Justice. 2013(53), pp. 339-342.

DiMaggio, J. A. Vernon, W. 2011. Forensic Podiatry: Principles and Methods. New York: Springer Science & Business Media.

Forensic Magazine. Considerations of Gait at Crime Scenes. [online] Available:

Jasuja, O. P. Manjula. Estimation of stature from footstep length. Forensic Sci Int. 1993(61), pp. 1-5.

New Scientist. Cameras Know You by Your Walk. [online] Available:

Stevenage, S. V et al. Visual analysis of gait as a cue to identity. Appl Cognitive Psych. 1999(13), pp. 513-526.

Facing the Facts on DNA Phenotyping

Facing the Facts on DNA Phenotyping

Last week a somewhat fascinating article was published by the New York Times discussing forensic DNA phenotyping, a new(ish) technique that allows for (as popular media would say) a person’s face to be reconstructed from only their DNA. It sounds almost science fiction-esque doesn’t it?

Media interest in the topic appears to have been resurrected over the last couple of months by the use of DNA phenotyping by law enforcement officers in Colombia, South Carolina, investigating the unsolved 2011 murder of Candra Alston and her daughter Malaysia Boykin. Investigators hired the services of an independent company to carry out DNA phenotyping on DNA recovered from the crime scene years before, resulting in the production of the apparent face of the suspect.

This is not novel, ground-breaking work. In fact the whole concept of this technique has been floating around for a few years now (though this was presumably the first case in which a face reconstructed solely from DNA was presented to the general public).


But just what actually is DNA phenotyping? As you may or may not recall, a phenotype is a physical characteristics which is the result of genetics, for instance the colour of one’s hair, eyes or skin. DNA phenotyping essentially attempts to determine physical traits such as these using only genetic material. This is based on the idea that certain genes are contributors to particular characteristics. Theoretically, this could be such a powerful tool for investigators, forensic, historical and medical investigators alike. Imagine a piece of software which is simply fed a DNA profile and spits out the face of your perpetrator (viewing it in a very black box manner of course). A face which could then be compared to existing mugshots of criminals or circulated to trigger recognition. Or the reconstructed face of a member of some ancient civilization. The possible applications are exciting and plentiful.

But it is of little surprise that, since the publication of this work over the last few years, numerous accounts emerged in the media blowing the results way out of proportion. If one were to Google DNA phenotyping, it is easy to believe it is a well-established technique often used in legal investigations around the world. In reality, this is a technique that is not permitted in court and in fact some countries have outright banned the use of DNA phenotyping (perhaps more for ethical purposes than concerns over accuracy). A research team at Penn State University in the US, led by Peter Claes and Mark Shriver, has been conducting research into this field of work. Despite the promising results published by the group, it has been made clear that the work so far provides an “analytical framework” but considerable further research is needed. Before any claims are made that scientists can reliably re-create a face from DNA, one must pay attention to the current lack of knowledge, inaccuracies and issues linked with DNA phenotyping, unfortunately often ignored by the media.

There are obviously clear ethical concerns associated with such techniques. Unsurprisingly, concerns over the possibility of racial profiling occurring have been raised. The images produced by DNA phenotyping methods have been referred to as being “generic” and could easily draw investigators down the wrong path as they focus solely on a particular physical characteristic suggested by this method. But on the other hand, could an eyewitness account, which are often famed for being ripe with inaccuracies, not also lead to such problems, should the eyewitness state the race of the person they saw?

Ethics aside, the accuracy of the technique is no doubt at the forefront of most people’s mind. Undoubtedly the face that is reconstructed can only ever be a kind of estimation based on the information available, being unable to take into account a whole array of factors that go beyond DNA. Dyed hair, hairstyle, facial piercings, tattoos, accessories, scars, even down to a person’s characteristic facial expressions which can wildly change the appearance of a face. Many genes are known to contribute to the development of a person’s face and the appearance of certain characteristics, and these genes can be targeted in this kind of work. But it does not take an expert in genetics to conclude that there are equally many genes that may contribute to appearance that we do not know about. So how accurate can this technique really be (at this point in time anyway)?  And regardless of the actual accuracies (or inaccuracies, if you wish) of this technique, somewhat equally as important is how people actually perceive it. Anyone with the slightest interest in forensic science is no doubt aware of the so-called “CSI effect”, which has raised concerns over how lay people perceive scientific (or sometimes even unscientific) techniques. Is it plausible that, should DNA phenotyping be accepted into a courtroom, members of the jury will see “DNA” and assume it must be just as trustworthy as established DNA profiling techniques?

Despite the possible benefits of this technique, there is ultimately currently no way only the DNA of an individual can be used to reconstruct their face.

Thus this is a technique still under research, not yet developed enough to actually be used in legal investigations. And yet, in the United States at least, various independent companies are offering DNA phenotyping services. The law enforcement agency referred to at the beginning of this post in fact used one of these services. The results of these companies list a range of biological and physical attributes, including sex, skin colour, eye colour, hair colour, probable ancestry, and even if the suspect is likely to have freckles! It has even been suggested that genetic analysis could be a predictor of a person’s age. There is an array of factors that can affect a person’s appearance that do not necessarily have anything to do with their genetics, and a person’s DNA can in no way account for this.

These facts by no means aim to take anything away from the technique. DNA phenotyping undoubtedly can unlock entirely new routes of investigation for law enforcement officers, and it has been successfully used in a number of cases. Even if its use would not currently be accepted as evidence in court, it may still provide law enforcement with new investigative leads if other lines of inquiry have been exhausted.

Although the concept of DNA phenotyping emerged years ago and made slow progress, in the last couple of years research and interest appear to have boomed. It is a fascinating topic with huge potential, but it is ripe with practical and ethical concerns that will no doubt bring about some very intriguing debates. I am sure we will be hearing much more about this in the coming years.


Claes, P. Shriver, M D. Establishing a multidisciplinary context for modelling 3D facial shape from DNA. PLos Genet. 10 (2014).

Claes, P. Hill, H. Shriver, M D. Toward DNA-based facial composites: preliminary results and validation. Forensic Sci Int Gen. 13 (2014), pp. 208-216.

New Scientist. Genetic mugshot recreates faces from nothing but DNA. [online][Accessed 02 Mar 2015] Available:

The New York Times. Building a Face, and a Case, on DNA. [online][Accessed 02 Mar 2015] Available: