(Forbes) Modern technologies can now detect and analyze DNA from samples comprised of only 16 cells. But due to the touch-transfer properties of DNA, determining how those cells reached the surface on which they were found is impossible. Tiny amounts of touch-transferred DNA have placed people at locations they had never visited and implicated people for crimes they did not commit.
Forensic technologies detecting and analyzing DNA evidence have been at the forefront of criminal investigations. Scientists have told us that the perpetrator of a crime will leave traces of his DNA at the crime scene, and if found in even in small amounts, the evidence can be used to identify the perpetrator. Finding a suspect’s DNA at a crime scene, on a victim, or on a piece of evidence, is consistently used by law enforcement to place a suspect at the scene of the crime, with the victim, or in contact with the relevant piece of evidence. Prosecutors have been representing DNA evidence as superior to all other types of identification evidence. However, research conducted at the University of Indianapolis shows that the detection of DNA does not actually indicate presence or contact. In fact, it may not narrow the scope of the investigation at all.
This is because humans shed DNA continuously, and shed DNA transfers freely between people and objects. DNA can be transferred through a handshake or touching an inanimate object, like a doorknob. Every time you shake someone’s hand you might receive some of your acquaintance’s DNA, and that of other people whose DNA had come into contact with your acquaintance’s hand. Scientists refer to this phenomenon as “secondary transfer DNA,” while journalists have been using the term “touch DNA.” I will use a more global term, “touch-transfer DNA,” to describe DNA transferring easily through contact or touch.
Imagine a man waiting at a restaurant for a business associate. His business associate opens the restaurant door, then walks over to the man and shakes the man’s hand with the same hand the associate used to open the restaurant door. The man has now received a DNA transfer of his associate’s DNA, and any DNA that the associate’s hand picked up on the restaurant door handle. If we were to swab the man’s hand for DNA, we might find the man’s DNA, his associate’s DNA, and the DNA of a few other unknown people who touched the door handle of the restaurant and whose DNA stuck around, people who the man never touched. The DNA of these other people transferred to the man’s hand through the touch-transfer properties of DNA.