New research finds that DNA forensics may not be as reliable as we once thought. Moreover, these newly established findings may lead the criminal justice system to change the way they use DNA to prosecute criminals.
Forensic scientist Cynthia Cale reported new findings on DNA forensics at the annual meeting of the American Academy of Forensic Sciences on February 21st, 2019.
Cale reported finding that a 10-second handshake could transfer one person’s DNA to another person, and by them, be transferred to an object that the other person never touched.
In handshaking experiments, individuals who had never picked up a knife became the primary source of DNA on the knife about seven percent of the time. Their DNA was transferred to the knife when their handshaking partner grasped the knife handle.
A different study, performed by Leann Rizor, a forensic anthropologist at the University of Indianapolis, found that the last person to come in contact with an object, such as a communal water container, often was not the person who left behind the most DNA.
These findings suggest that even brief contact between people, or with an object, could spread a person’s DNA to objects and places that they’ve never even come in contact with. This could easily complicate crime scene investigations. And while the results don’t necessarily mean that DNA evidence is unreliable, it does indicate that investigators must be especially careful to account for accidental transfers.
Geneticist Mechthild Prinz of John Jay College of Criminal Justice in New York City says that in real-world situations, it’s likely unusual to find people’s DNA in places or on objects they’ve never come in contact with. “We can’t discount [the idea], but we shouldn’t use it to throw the evidence out in every single case,” she told ScienceNews.
Cale, of the Houston Forensic Science Center, previously found that shaking hands for two minutes could transfer a person’s DNA to an object via the other person’s hand. However, critics were quick to point out that two minutes is an unrealistically long time for a handshake. This led her to shorten the handshaking time to 10 seconds in her new experiments. She also adds that even shorter contact between people could transfer DNA.
In the experiments conducted by Rizor, four University of Indianapolis students gathered around a table and poured themselves drinks from a communal pitcher. Other students were present to watch the experiment and were free to leave the room, talk, and move around. This was intended to simulate conditions within a restaurant.
As each of the students at the table handled the pitcher and their plastic cup, researchers swabbed the pitcher’s handle, the plastic cups, and the students’ hands for DNA.
The researchers found that DNA from each of the students at the table was present on the pitcher’s handle and on each of the students’ cups, even though the students only handled the pitcher and their own cup. Furthermore, DNA from the observing students in the room showed up on the swabs, even though none of the observers had touched the students at the table nor the pitcher or cups.
Researchers couldn’t determine the last person to handle the pitcher, nor how long a student touched the pitcher or cup by looking at the amount of DNA left on the objects. Rizor pointed out that the results demonstrate that DNA can transfer easily and unpredictably in social settings.
“Some of those results may be explained because people shed DNA at different rates,” Prinz told ScienceNews. “But it’s still not clear how often that type of transferred DNA might skew crime scene investigations. We’re all still trying to get a handle on how realistic this is.”
But as scientists explore how this type of transferred DNA could affect crime scene investigations, innocent people are being convicted of crimes that they did not commit, and DNA evidence is the catalyst.
DNA forensics have been used to help prosecute criminals since 1986, and it’s unknown how many times the DNA forensics have aided in convicting the wrong person for a crime. Just three years after the introduction of DNA to the criminal justice system, the first DNA exoneration took place. And to date, 364 people have been exonerated after DNA evidence was improperly used to convict them of a crime.
As more research surfaces about the unpredictability of DNA, critics of DNA forensics wonder if the findings will change the way DNA evidence is used in the criminal justice system.