A 32-year-old murder case that many considered unsolvable has finally been resolved – and it all boiled down to the equivalent of just 15 human cells.
While the techniques that made this possible are not new, what made this case truly extraordinary was the amount of DNA available: only 0.12 nanograms. That’s less than in any case in history – to put the achievement into perspective, the amount of DNA used by commercially available tests is around 750 to 1,000 nanograms.
Stephanie Isaacson was only fourteen when she was sexually assaulted, beaten and strangled to death on the way to school. DNA evidence of his killer has been left on his shirt, but several attempts over the years to find a match have been unsuccessful. For more than three decades, his case was cold.
However, nine months ago, a Texas-based genome sequencing company called Othram approached the Las Vegas Metropolitan Police Department (LVMPD) with an offer. They had recently received an anonymous donation to use to fund the investigation of a cold case. It didn’t matter which, as long as it came from LVMPD.
“Stephanie’s case was chosen specifically because of the minimal amount of DNA evidence available,” LVMPD Lt. Ray Spencer told a press conference. press conference concerning the discovery. “As a result, we have identified Darren Roy Marchand, who was positively identified as the person who sexually assaulted and murdered Stephanie in 1989.”
DNA analysis has come a long way in the past decades. What was once the preserve of science fiction can now be purchased as a (sometimes misguided) birthday present. These commercial DNA tests don’t just tell you about your ethnicity or medical predispositions – they’re being used in medical research, they’re helping beat the coronavirus pandemic, and, yes, they even fight crime. In 2018, for example, genetic genealogy techniques helped catch the Golden State Killer who murdered 12 people and raped 51 others in the ’70s and’ 80s.
Isaacson’s killer was identified using a similar technique. For seven months, Othram built a genetic profile from the remnants of DNA evidence, which they compared to ancestry databases. They were able to match the DNA to the cousin of the alleged murderer of Isaac, and from there they identified the killer himself – a man previously accused in 1986 of strangling 24-year-old Nanette Vanderberg to death ( this case was dropped for lack of evidence, and the suspect committed suicide nine years later).
“When you can access information from such a small amount of DNA, it really opens up the possibility for so many other cases that have historically been considered cold and intractable,” Othram chief executive said. , David Mittelman. BBC.
While there is no way of knowing if Isaacson knew his killer, Lt. Spencer said it was a random attack – known to decrease considerably the chances of closure.
“I’m glad they found out who murdered my daughter,” Isaacson’s mother wrote in a statement read at the press conference. “I never believed the case would be solved.”
THIS WEEK IN IFLSCIENCE
Get our greatest science stories delivered to your inbox every week!