Cracking cold cases with DNA analysis and old fashioned police work
Alex Brockman | CBC News | Posted: February 13, 2016 3:09 AM | Last Updated: February 13, 2016
'The DNA does not change'
Police investigators pore over crime scenes looking for anything that might lead them to a criminal, but sometimes their hunt can be limited to tools they use.
That happened in Windsor, Ont. in a series of sexual assault cases in 1990. Women were attacked in the city's east end as police spent months investigating five separate rapes believed to be committed by the same person. That person was never charged.
Then, because of new technological advances in DNA testing, forensics specialists were able to bust the case open after 25 years. Reanalyzing evidence from the cold case, forensics specialists drew a hit on the national DNA databank and arrested a 54-year-old man who had since moved to Burnaby, B.C.
Police are looking for possible connections between that person and those unsolved rapes from that same summer.
This case is just one example of how police forces are using a combination of modern technology and old fashioned police work to crack open unsolved cold cases.
While all unsolved cases are reviewed periodically, cases can sometimes be picked out based on a hunch, or a small piece of evidence that was overlooked.
"Many times with cold cases, a tip or piece of evidence may come in that might pique someone's interest," Sgt. David DeLuca told CBC News. "You may get a tip from any number of sources which may redirect you back to someone who was a suspect at the time … at that time it didn't seem important, but now it is."
While not speaking directly about the ongoing sexual assault case, DeLuca has been with the Windsor police for more than 20 years and has spent five years in his career working with the forensics evidence unit.
"It's not always just DNA evidence, sometimes it's witness evidence," DeLuca said. "Someone will give you information about what they saw they didn't think was important back then and suddenly it turns out that was very important."
Before taking over the unit in 2015, DeLuca was a constable in forensics from 1998-2003. At the time DNA analysis was just taking off.. He's characterized the technological changes as "amazing."
Nobel Prize winning technology
Sashi Jasra, the program chair of forensic sciences at the University of Windsor said one of those relatively new techniques is called the polymerase chain reaction (PCR). The team of scientists who discovered this won the Nobel Prize for chemistry in 1993.
It allows DNA samples to be replicated and amplified, meaning analysts can do more with less in identifying a sample.
"In forensic cases, the criminal is not going to come back and give you more of his or her samples," Jasra said.
"DNA does not change," she said. "For so many years back, for a case where there are bone remains, dental remains, even if a few teeth are they. They can get to the root of a tooth and they can get the DNA out of that."
But DNA evidence only goes so far, DeLuca said. It can only prove that a sample from the crime scene came from a particular individual. Finding and linking a suspect to crime ultimately comes down to old fashioned detective work.
"Investigators never forget about a case, I can tell you that," DeLuca said. "They constantly review evidence, things are never forgotten. It may take a long time to get back to a case, but eventually everything gets revisited."