Advanced testing techniques, combined with a more sophisticated judicial system, have led to more frequent use of DNA evidence in crime cases. At the same time, courtroom challenges by defense attorneys are moving away from the validity of DNA toward handling, testing and lab work.
Scott McBride, a Columbia attorney who has handled six capital murder cases involving DNA evidence, said between being “tagged, bagged and stored” by police to crime lab testing, DNA samples often pass through many hands, leaving room for contamination or mishandling.
When and how DNA evidence is collected and disclosed by police and prosecutors would change under a bill presented to the Missouri General Assembly. The Integrity of Justice Act would require the preservation of DNA evidence gathered in all felony cases, rather than just the most serious.
Jurors might not totally understand DNA, said Cary Maloney, a specialist with the Missouri Highway Patrol’s crime lab, but they accept it as reliable evidence in court. And because just a few microscopic skin cells can point to a culprit, evidence doesn’t have to come from body fluids anymore.
“Skin cells rub off easily and are constantly regenerating,” Maloney said. “It takes a mind shift. (Investigators) have to stop thinking, ‘I’m looking for stains,’ and start thinking about things an individual might have come in contact with.”
DNA is essentially a strand of nucleotides inside each living cell, linked together in a pattern unique to an individual. While the total amount of DNA in each person’s body is unique, not all links on a DNA strand will differ from one person to the next.
The Missouri Highway Patrol uses Short Tandem Repeat (STR) analysis to examine 13 specific areas on DNA strands that are most likely to differ among individuals. It’s not impossible for one random individual’s DNA pattern to match another’s all 13 times, but the odds against it are usually in the trillions, Maloney said.
In defending against such odds, McBride said, defense attorneys must look at all the lab’s raw testing data. If mishandling of DNA evidence is suspected, it’s important to enlist an expert’s help in wading through all the data, he said.
“What’s a match may be subjective, depending on the lab’s policies,” McBride said. “What one says is a match, another might not.”
McBride said many jurors use television shows such as “CSI” as a reference point for considering DNA evidence. Time-consuming testimony about the handling and testing of DNA doesn’t seem to bother them, he said.
“In life-or-death cases, I think jurors want to make sure they’re doing the right thing,” McBride said. “But DNA is powerful evidence if presented well. Ignore it at your peril.”
Columbia police are currently trying to link a suspect to a string of up to 40 local burglaries with evidence that includes blood found on broken windows, sweat from a hat brim and even a discarded napkin.
Sgt. Stephen Monticelli, an investigative supervisor with the Columbia Police Department, said local officers routinely collect DNA evidence at all violent crime scenes.
“Every day we’re clearing cases with DNA,” Monticelli said. “It’s a tremendous tool.”