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.

 

References

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: http://www.bbc.co.uk/news/science-environment-19412819

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.

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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.

References

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: http://upoa.biz/dna-testing

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

Synopsis

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.