Shreds of Evidence Are Not Always Reliable
A defense attorney representing an Oklahoma City police officer facing six counts of first-degree rape told jurors a woman’s DNA found inside the officer’s pants is not evidence that he raped her.
“It’s transfer DNA,” the attorney argued in the November, 2015 trial of Daniel Holtzclaw.
Whether the DNA transfer defense will open a path to acquittal remains to be seen. The DNA evidence is only one aspect of a case that also includes victims’ testimony and GPS data about the officers’ location at times when 13 women allege he assaulted them.
The DNA transfer argument, however, reveals cracks spreading across the surface of forensic science that until recently was often considered to be rock solid.
In the September, 2015 Journal of Forensic Science, researchers from the University of Indianapolis Molecular Anthropology Laboratory found test subjects’ DNA on knives they had never touched. It did not happened just a few times – it happened in 85 percent of the tests.
The experiment required subjects to shake hands for two minutes with a person who later handled a knife. On five of the knives, the only DNA or the largest portion of DNA found belonged the person who had not touched the knife.
In the Oklahoma City case, an attorney argued that the officer had been in contact with the woman whose DNA was found in his pants. Her DNA transferred to the inside of his pants when he went to the restroom, the attorney suggested.
DNA Does Not Spell Guilty
It is not the first time a DNA transfer theory has been offered in a high-profile case. In 2001, a respected Massachusetts doctor and adjunct Harvard professor was convicted of murdering his wife during an evening walk. Dirk Greineder’s attorneys argued secondary transfer was responsible for DNA identified on a knife and gloves found near the murder scene.
The Massachusetts’s doctor’s attorneys told jurors his DNA ended up on his wife’s face because they shared a towel. His DNA transferred to the crime-scene evidence when it came into contact with her face, they argued.
Although jurors were not persuaded by the argument, the September JFS article contributes to growing body of research that could prove more persuasive to future juries. Much research to date has acknowledged multiple sources of DNA can be found on objects, but researchers have said the majority of DNA found typically belongs to the last person who touched the object.
Arguments about what is “typical” are a far cry from the billionth-degree of certainty jurors were once asked to attribute to DNA evidence. Research that supports experts’ knowledge of typical circumstances has only scratched the surface of how DNA might migrate in real world circumstances.
In a 2010 University of North Texas masters thesis, Shamika Kelley investigated how DNA might be transferred by “donors” who engage in conduct likely to transfer higher volumes of DNA. Donors licked their thumbs as a person might when turning pages in a book or counting paper money. Others placed a pen in their mouth that was then placed in the palm of “vectors” who handled objects.
In the majority of those experiments, the secondary donor contributed more DNA than the person who actually handled the object. In every case, the amount of DNA recovered was minimal.
The tiny amounts of DNA used to construct broad theories about who likely touched an item are the reason touch DNA evidence is likely to face increasing scrutiny. Unlike early DNA science, new techniques let laboratories amplify the most minuscule amounts of DNA.
We All Leave a Little Wherever We Go
Those amplified pictures of minuscule DNA samples are often propped up in court by a rhetorical platform planked with Locard’s Exchange Principle. A pioneering forensic scientist recognized as France’s Sherlock Holmes, Dr. Edmond Locard authored the crime-scene axiom that says every perpetrator leaves something behind.
What the emerging science of secondary DNA transfer tells us is that perpetrators are not the only ones who leave something behind. Every where we go, we all leave tiny traces, which can then be transferred to other objects we have never touched. The implications can be disturbing if juries are persuaded that DNA typically spells guilt.
In 1996, the Canadian Society of Forensic Sciences Journal published a study that showed how sperm cells could be transferred in a washing machine to new, unstained garments – even in the next wash cycle. An August, 2006 Edition of Journal of Forensic Identification revealed how background DNA from forensic laboratories could contaminate crime-scene evidence.
By the pathways described in those articles, an innocent bystander whose DNA was transferred to a scene before a crime occurred could be implicated by DNA smeared around a forensic laboratory. A person who launders their clothes in an apartment-complex laundromat could be wrongly implicated in a sex crime.
Prosecutors often prefer forensic science not because it is reliable but because it is persuasive. When confronted with forensic evidence, a defendant needs a defense attorney who can establish, through science, that forensic testimony is not as reliable as prosecutors would have juries believe.
Free Consultation: Tulsa Criminal Defense Lawyer
If you are charged with a crime in Tulsa, you need an attorney who knows how to examine the evidence prosecutors will use against you. For a free consultation with a Tulsa criminal defense lawyer, call Wirth Law Office at (918) 879-1681 or email your question to me using the form at the top of this page.