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: Eyewitness Testimony & The Ronald Cotton Trial

Forensic Failures: Eyewitness Testimony & The Ronald Cotton Trial

Eyewitness testimony is far from being a form of scientific evidence and is in fact based on perhaps one of the most flawed tools available: human memory. Despite this, the testimony of eyewitnesses can still have an enormous bearing on the outcome of a criminal investigation but unfortunately, as we will see, this evidence can range from being mildly misleading to catastrophically incorrect. And when it is the matter of someone’s life and freedom on the line, the criminal justice system cannot afford to get it wrong.

So let’s delve into a case that shows some of the great flaws of eyewitness accounts and how they can lead to devastating consequences if not treated with care.

The Case

One night in North Carolina in 1984, 22-year-old student Jennifer Thompson lay unsuspectingly in her bed when an assailant broke in, held a knife to her throat and raped her. During the ordeal, Thompson decided that she would try to remember as much about her attacker as she could, hoping to run straight to the police and get this man identified. So she took in everything she could about his face, skin colour, hair, height, weight and voice. She was convinced that she had etched this person’s image onto her brain.

Later at the police station, an investigating officer sat down with Thompson and the two of them produced a composite sketch of the rapist. This was enough for police to round up potential suspects. Thompson was later presented with a police line-up of six men (first by photograph and later a physical line-up), from which she picked out with “100 percent certainty” her attacker – a man named Ronald Cotton.

“Looking at a series of police photos, I identified my attacker. I knew this was the man. I was completely confident. I was sure”.

The suspect fit her description perfectly and he was already known to the police following a few other legal incidents, including attempted rape when he was 16. Cotton was tried, a trial at which Thompson looked him dead in the eye and declared that this was in fact the man who had raped her. Based on the victim’s testimony, and other pieces of circumstantial evidence, he was found guilty and sentenced to life imprisonment.

Meanwhile in the prison where Cotton was being held, another inmate eventually joined the ranks, a man named Bobby Poole. Poole had been convicted of a series of violent rapes and was serving consecutive life sentences. Incidentally this man bore a striking resemblance to Cotton, so much so that prison staff were constantly getting them confused. Any alarm bells ringing? Cotton subsequently confirmed his suspicions and discovered that Poole was in fact the actual rapist of Thompson. This was enough to win Cotton a retrial, but when presented with the two men, Thompson once again stated that Cotton was the attacker and she had never before seen Poole, her actual attacker. Fortunately Cotton’s break came in 1995, when he heard about a new technique known as DNA analysis. Using a semen sample collected from Thompson at the time of the attack, DNA evidence was able to prove that Cotton was innocent and Poole was the actual rapist. Case closed.

The Problems with Eyewitness Identification

The consequences of mistaken identification can be disastrous, and the people affected by this error is larger than one might initially think. In this case, an innocent man of course spent over a decade of his life behind bars for a crime he did not commit, the implications of which do not even need to be stated. The victim must then live with the knowledge that, firstly, she is in a way responsible for the incarceration of this innocent man and, secondly, her actual attacker has been on the loose! Not to mention the effects on the family of both the victim and the wrongly accused. The range of those affected can then extend to anyone who has since been the victim of the actual criminal. In this case Poole went on to rape a series of women, crimes which perhaps may not have occurred had Cotton not been wrongfully charged, forcing police to continue their investigation.

So just how can a case of mistaken identity occur?

In this instance, the assailant was mere inches away from the victim’s face for a considerable length of time (a length of time that no doubt felt like a lifetime), and yet she still made an incorrect identification. How could this happen? There are a number of factors which are known to reduce the accuracy of eyewitness identifications, many of which can into play in Thompson’s case. Extreme stress when viewing the perpetrator and the presence of weapons at the scene can affect a person’s ability to remember and recall, as can racial differences between the perpetrator and the witness. A suspect’s lack of distinctive characteristics will render them more difficult to remember, and of course the person may be wearing some kind of disguise to hide their features. The viewing conditions can drastically affect eyewitness identification too, such as the distance between the witness and the suspect, the lighting in the environment, and the length of time the witness sees the suspect (Ellis et al, 1977). In the United Kingdom following a case in 1977 (R v Turnbull), a set of guidelines relating to cases involving eyewitness testimony were introduced. These guidelines were intended to assist members of the jury in treating eyewitness evidence with the care and attention required, taking into account the circumstances surrounding the identification by the witness.

Then there are the biases that can occur as a result of the management of the investigation. The police line-up itself can introduce prejudice from the start. Had it been somehow suggested to Thompson that the perpetrator was definitely somewhere in the line-up, she may have been far more likely to choose someone even if, as in this case, he was not actually there. The process of merely being asked to choose from a selection of faces can force people to choose incorrectly. Admittedly, Cotton and Poole did look very similar at first glance, just as many people in the world share looks to a certain extent. So in Cotton’s retrial, why would Thompson still point the finger at Cotton when her real attacker was stood right there? Because reinforcement can alter memory. After years of her positive identification of Cotton being reinforced, her memory had replaced her real rapist’s face with Cotton’s. Human memory is a funny old thing, and certainly can’t necessarily be trusted.

The eyewitness statement of a witness or victim is certainly not evidence based on science, and yet this evidence can often carry such weight that the pointing finger of a witness may as well be an airtight scientific report. The Ronald Cotton case was not a one-off incident in which eyewitness testimony failed. The list of cases of people being wrongfully convicted based on eyewitness testimony, only to be later exonerated, is far longer than it should be (in fact the Innocence Project states that eyewitness misidentification has played a role in over 70% of convictions which were later overturned by DNA evidence). Looking at all the flaws of eyewitness testimony and all the cases of wrongful conviction based on it, it makes you wonder whether eyewitness testimony has any place in the courtroom at all.


Eliis, H. D. et al. Experimental studies of face identification. Journal of Criminal Defense. 1977(3) pp. 219-234.

Hansen, M. Scoping out eyewitness ids. Am Bar Assoc J. 2001(87).

New York Times. ‘I was certain, but I was wrong’. [online] Available:

Scientific American. Why science tells us not to rely on eyewitness accounts. [online] Available:

Colin Pitchfork & The Début of DNA Fingerprinting

Colin Pitchfork & The Début of DNA Fingerprinting

DNA fingerprinting, the process of producing a unique ‘fingerprint’ from a DNA sample, is something of a staple in forensic science. The ability to link a suspect to a crime scene or identify a set of remains has revolutionised legal investigations, being utilised in countless legal cases across the world since its discovery in 1984.

But once upon a time this renowned technique was just emerging, with its creator, geneticist Sir Alec Jeffreys of the University of Leicester, still unaware of just how beneficial his new technique would be to the criminal justice system. But how did this somewhat stumbled upon discovery end up becoming one of the most reliable forensic techniques available?

The story begins in late November 1983. 15-year-old Lynda Mann set off from her home in a small Leicestershire village to visit a friend, but unusually did not return. The following morning her raped and strangled body was found on a quiet footpath. Little evidence could be found other than a semen sample retrieved from her remains, though even this proved to be ineffective in leading investigators in the right direction.

But this would not be the last the world would hear of Lynda Mann. Just a few years after Lynda’s murder, another young girl went missing in July 1986. 15-year-old Dawn Ashworth had been walking home when she disappeared, her family’s worst fears soon confirmed when her brutally raped and strangled body was found two days later in the woods. Once again, a semen sample was found on the victim. The similarities between the two murders were not overlooked and, with a fresh influx of interest and evidence, the investigation could progress, with police believing the same man could be responsible for both crimes. Suspicion soon fell on Richard Burkland, a 17-year-old local who appeared to have suspicious knowledge of the latest incident. Under questioning he admitted to murdering one of the victims. Job done, the police might have thought.

Meanwhile at the University of Leicester Sir Alec Jeffreys and his team were working on a novel DNA fingerprinting technique. The technique had already been utilised in an immigration case involving a boy from Ghana, successfully proving that he was in fact the son of a family living in the UK. Recognising the potential power of this procedure and keen to apply it to a criminal case, investigators pulled Jeffreys’ and his new technique into the case.

Contrary to the belief of police, DNA profiling actually proved that Richard Burkland’s DNA did not match the semen found at the two crime scenes, pushing the investigation back to square one. Although this in itself was a ground-breaking scenario, the first ever exoneration of an innocent man using DNA fingerprinting, the murderer was still at large and the police had no more leads to follow.

With no other options, on 1st January 1987 Leicestershire Constabulary announced that they would be joining forces with the Forensic Science Service to conduct a huge DNA profiling project, collecting DNA samples from over 4000 local men in order to rule them out as suspects. However six months down the line a match had not been found. Were their efforts all for nothing?

Fortunately, a lucky break came from a particularly interesting conversation overheard in a local pub. Ian Kelly, an employee at a nearby bakery, was caught bragging about being paid £200 to submit a DNA sample on behalf of a work colleague. Living too far away from the area to have been required to give a sample himself, Kelly had apparently agreed to this request without many questions. Unsettled by the conversation, another employee soon raised the alarm, and Kelly was detained and questioned.

Kelly was covering for Colin Pitchfork, a local baker. Pitchfork had convinced Kelly that he would be framed for murder if his own blood sample was submitted, a story which was evidently enough to persuade Kelly to oblige.

On 19th September 1987, Pitchfork was arrested. After the new DNA profiling technique matched his DNA fingerprint to the crime scene samples, he admitted to raping and killing the two girls. Experts calculated the probability of this match occurring by chance to be 5.8 x 10-8. Pitchfork was sentenced to life imprisonment on 23rd January 1988.

Moral of this story – if you think you’ve gotten away with murder, you had better hope your mates don’t chat about it at the pub.


Bodmer, W. F. et al. 1994. The Book of Man: The Human Genome and Our Quest to Discover our Genetic Heritage. Oxford: Oxford University Press.

R v Pitchfork 2009

Featured Image: DNA Testing. [online] Available:

Code of a Killer Competition

Earlier this week the much-discussed Code of a Killer aired in the UK, an extraordinary movie based on the true story of scientist Alec Jeffreys and the discovery of DNA fingerprinting. The DVD will be released on 20th April 2015, but until then we have a fantastic competition to win a copy. See below for details on how to enter.

COAK DVD 3D_small


From the Director of Broadchurch and the producer of Line of Duty comes Code of a Killer, out to own on DVD April 20th. The gritty telling of the extraordinary true story of Alec Jeffreys’ discovery of DNA fingerprinting and its first use by Detective Chief Superintendent David Baker in catching a double murderer.

David Threlfall (Shameless) takes the role of David Baker who, between 1983 and 1987, headed up the investigation into the brutal murders of two Leicestershire schoolgirls, Lynda Mann and Dawn Ashworth. Only a few miles away, Dr Alec Jeffreys, played by John Simm (Prey), was a scientist at Leicester University who, on 10 September 1984, invented a remarkable technique to read each individual’s unique DNA fingerprint.

COAK DAVID 12 copy

If you didn’t have chance to catch it on TV, Code of a Killer will be released on DVD on 20th April. Click here to pre-order your own copy from Amazon now!

Competition time! Want to win your own copy of Code of a Killer? Then simply head on over to Twitter and retweet the below message to be in with a chance to win. Please note this is only open to those in the UK.

Forensic Case Files: Bruce Ivins and the Anthrax Attacks

Forensic Case Files: Bruce Ivins and the Anthrax Attacks

In September 2001, when the US was still reeling from the notorious 9/11 terrorist attacks, two US Senators and various media organisations were sent letters containing spores from the bacterium Bacillus anthracis, the cause of the disease Anthrax. The malicious mail resulted in the deaths of five people, the infection of 17 others and an investigation between the FBI and the US Postal Inspection Service that spanned almost 7 years.

Bacillus anthracis is a rod-like bacterium which can, upon entering the body, bring about the acute disease known as Anthrax. The endospores (spores) of the bacterium can lay dormant for years, but become activated and multiply after coming into contact with a host. Once contracted, the symptoms of the disease are dependent on the route by which the bacteria entered the body. However left untreated, the disease can ultimately kill the host.

The mailed anthrax spores were accompanied by misleading letters suggesting the attack was motivated by religion, though the prospect of terrorist groups, that were already at the forefront of the country’s mind, were soon discounted. It was soon concluded that a likely source of the anthrax, which was of the Ames strain, had been maintained by the US Army Medical Research Institute of Infectious Diseases (USAMRIID). Suspicion fell on Dr Bruce Ivins, who had been a researcher at the facility. Whilst in this position, Ivins had created and maintained this particular spore-batch, suspected to have been the batch used in the anthrax attack. With suspicions supported by an array of incriminating circumstantial evidence, investigators called upon a team of scientific experts to establish whether there was a link between Ivins’ own anthrax and the mailed anthrax.


Traditional forensic techniques were used in the examination of the spore powder and the letters and envelopes, including fingerprinting, and hair and fibre analysis, though this did not lead to any major breakthrough. A suite of analytical techniques was employed to ascertain various facts regarding the anthrax. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to identify the size, shape and quality of the anthrax spores, as well as provide a profile of the chemical elements within the spores. SEM and TEM are microscopy techniques which employ a focused beam of electrons which interacts with the atoms of the sample, allowing it to be visualised. They can be coupled with energy-dispersive X-ray (EDX) spectroscopy to provide elemental analysis. The physical and chemical characteristics of the spores allowed investigators to presume that the anthrax was not weapons-grade, but it was of a concentration and quality similar to that used in bio-defence research.

Inductively coupled plasma optical emission spectroscopy (ICP-OES), a technique based on the emission of photons from substances, was used to provide further details of the elemental composition of the spore powder. Furthermore, gas chromatography mass spectrometry (GC-MS) was employed to characterise the spores. Experts at the Center for Accelerator Mass Spectrometry (CAMS) were called upon to analyse the anthrax spores and establish their relative age. Accelerator mass spectrometry turns a sample, which has been converted into solid graphite by the analyst beforehand, into ions and accelerates these ions to high kinetic energies before conducting mass analysis to detect C14 (and potentially other isotopes depending on the work) to estimate the age of a sample. The analyses carried out on the samples in this instance determined that the mailed anthrax has been produced within 12 months of the attack, narrowing down the possible sources and suspects.

But perhaps the biggest breakthrough in the case came from a newly developed DNA fingerprinting technique which allowed investigators to conclude that the blend of anthrax spores created by Ivins in the lab was identical to that used in the attack, though how unique this “genetic signature” was has been somewhat debated. The US Justice Department later concluded that Ivins was solely responsible for the preparation and mailing of the deadly spores, claiming that he believed the scare would resurrect his anthrax vaccine program. Ivins later died from an overdose, deemed to be a suicide.

The case of Dr Ivins and the anthrax letters is a great example of how different analytical techniques can be drawn together to work in perfect harmony, utilising their individual powers to find out everything there is to know about a sample. In this case the array of techniques used allowed investigators to discover what the spores looked like and what they were composed of, their concentration and quality, and even how old they were. Armed with this information, investigators could home in on the source of the anthrax spores and the man behind the attack.


Centre for Infectious Disease Research and Policy. FBI says it easily replicated anthrax used in attacks.

US Department of Justice (2010). Amerithrax Investigative Summary. Darby, PA: DIANE Publishing.

Washington Post. FBI investigation of 2001 anthrax attacks concluded; U.S. releases details. [online] Available:

Forensic Failures: DNA Evidence and the Phantom of Heilbronn

Forensic Failures: DNA Evidence and the Phantom of Heilbronn

In 1993, the existence of a brutal murderer came to light when an elderly woman was strangled with a length of wire and left for dead in Germany, the perpetrator leaving behind nothing more than DNA on a teacup. The criminal did not stop there, and over the next decade and a half a sequence of crimes ensued, ranging from murders to car thefts to household burglaries. What did this string of ruthless attacks and petty crime have in common? Very little, with the exception of DNA from one individual recovered at each scene. A total of around 40 crime scenes all pointed to the same culprit.

Analysis of the DNA revealed the serial killer to be, somewhat surprisingly, a woman. Analysis of mitochondrial DNA indicated that the sinister suspect was most likely of Eastern European or Russian descent, narrowing down the list of suspects but not nearly enough. A bizarre picture of this woman began to form. The notorious killer became known as the Phantom of Heilbronn, a fiendish criminal with a 300,000 euro reward on her head. Also known as the Woman Without a Face, Germany’s most dangerous woman was responsible for the murder of half a dozen people… but also had a soft spot for theft?


It sounds like a baffling crime fiction novel in which the killer is never brought to justice, slipping through the net and always staying one step ahead of the perplexed police. However there is one slightly twist to this tale… the Phantom of Heilbronn was indeed never found, and a few years ago German police made a somewhat embarrassing confession… they had been pursuing a non-existent serial killer for 16 years. The Phantom of Heilbronn did not exist.

But how could this be? A series of vicious crimes and evidence of a single perpetrator at every scene, it seems like a reasonable assumption that this was the work of the same person. And this is just what investigators believed for a rather long time.

However suspicions were raised during the investigation of a person who had died in a fire, at which point the DNA of the “serial killer” was found on the body when attempting to identify the victim. The victim transpired to be a male asylum-seeker, so why had female DNA been recovered from the scene? This was bizarre enough, but even more so when subsequent tests (presumably using different swabs) failed to find the DNA again.

It soon came to light that police had been following the wrong scent, and suspicion soon fell elsewhere… cotton swabs. It eventually emerged that the DNA recovered from all of these crime scenes belonged to none other than an unsuspecting woman working in a swab factory in Bavaria, a factory which happened to have numerous Eastern European women on its staff (at least part of the serial killer profile was right). And so the mystery of the Phantom of Heilbronn was solved. Investigators had been collecting samples from numerous crime scenes using cotton swabs inadvertently contaminated with the DNA of a slightly careless factory worker. No doubt there were some red faces the day this little tidbit of information came to light!

So how could something quite so farcical occur in the first place? Let’s review the facts. We have a female serial killer, unusual in itself (women account for about 9% of serial killers, according to research carried out by Radford University), but not unheard of so no suspicions were raised there. The crimes appeared to cover all manner of sins, from murder to drugs to burglaries. Perhaps a little unusual, but theories began floating that the suspect was a drug addict or homeless person who would stop at nothing to steal some quick cash to get their next fix. This criminal’s DNA was found in all sorts of bizarre places, including on the remains of a cookie and on a toy gun. The wrongdoings spread over a decade and across three different countries, never leaving behind anything else that might point to the identity of the culprit. One would assume this took the homeless woman theory out of play – there are probably not many people living on the streets who have the funds to hop from country to country on a crime spree. In short, this phantom was one busy woman who liked to travel and mix up her wrongdoings!

Sounds somewhat ridiculous in hindsight. So why did it never occur to anyone that perhaps something else was afoot? After spending so many years tracking this villain, perhaps the concept of her not actually existing was impossible to comprehend. Investigators had spent years trying to get inside this woman’s head and figure out her motives, and the evidence was there to support their (slightly farfetched) theories. If nothing else, this highlights the dangers of being too committed to one line of evidence. It’s a very real problem for investigators and scientists. Once a hypothesis has been developed and a person genuinely believes in this theory, it is very easy to ignore subtle (or not so subtle!) indicators that the precious theory might be wrong. Suddenly, all evidence and results can be twisted to fit the theory, whether ludicrous or not. Not great scientific analysis, but it happens.

The case shed light on the fallacies of forensic evidence, even those which we tend to place great faith in. DNA evidence is perhaps viewed as one of the more reliable practices in forensic science, provided the appropriate procedures are followed (did these investigators even run control samples?). But at the time DNA analysis was something of a forensic holy grail, certainly not a technique which would draw investigators down the wrong path for over a decade. Yet from this incident, and many others since then, it is clear that even the best of techniques and practices must be accompanied with sound logic and an open mind.

As embarrassing (if slightly amusing) as this case might be, it highlighted some very real issues. To be sent back to some laboratory basics – know your equipment, always run controls and follow the results, not your hypothesis!

Putting aside the shame-faced investigators, the millions spent, the dozens of investigations affected and the police hours wasted, it at least makes for an interesting cautionary tale to tell budding forensic scientists for years to come.


BBC News. ‘DNA bungle’ haunts German police. [online][Accessed 23 Mar 2015] Available:

The Guardian. DNA analysis: far from an open-and-shut case. [online][Accessed 23 Mar 2015] Available:

Time. Germany’s Phantom Serial Killer: A DNA Blunder. [online][Accessed 23 Mar 2015] Available:,8599,1888126,00.html

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: