DNA evidence has become increasingly important in the criminal justice system over the past several decades, but experts say recent advancements in the field have made it much easier to extract biological material from smaller samples.
Mark Desire of the New York City chief medical examiner’s office discussed some of the practical applications new technology provides investigators, according to the New York Post.
“Back then, if we had a blood or semen stain at least the size of a nickel, we attempted to extract DNA from it — but we needed that much,” he said.
Desire, who serves as assistant director of the agency’s Department of Forensic Biology, reported that subsequent advancements now mean scientists can analyze samples as small as a pinhead.
“Until around 2005, the sample from which DNA was derived needed to be visible for us to have the best chance.”
He explained that those technological breakthroughs in the field have even more real-world implications for victims like a Yale student who was raped in 1994. Her attacker went free for decades until a small sperm sample from the case was treated with new processes able to yield results where prior attempts had failed.
First, Desire said the evidence was analyzed through automatic differential extraction, a process that separates material belonging to the victim from that of the suspect.
The isolated sperm cells were then opened to release the DNA inside. That evidence was finally repeated via polymerase chain reaction, by which a machine copies small samples of biological information, often until there is sufficient material to form a DNA profile.
When laboratory advancements provided investigators with a usable sample, they then turned to another important technological achievement — a DNA database containing references for all prisoners. A search against this database reportedly identified the attacker as James Edward Webb, currently serving an extended sentence on other charges related to rape.
“Improved DNA technology has brought closure to a lot of families,” Desire explained. “It’s helped us to solve cases that we never had hopes of solving in the past.”
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