The 1989 murder of a 14-year-old girl in Las Vegas was solved using what experts say was the smallest amount of human DNA ever to solve a case.
The Stephanie Isaacson murder case remained cold until new technology tested what little of the suspect’s DNA was left – the equivalent of just 15 human cells.
Police said Wednesday they identified the suspect using genome sequencing and public genealogical data.
Her alleged murderer died in 1995.
“I’m glad they found out who murdered my daughter,” Stephanie’s mother wrote in a statement that was read to reporters at Wednesday’s press conference.
“I never believed the case would be solved.”
Thirty-two years ago, Stephanie’s body was found near the route she normally took to school in Las Vegas, Nevada. She had been assaulted and strangled.
This year, the police were able to take over the case after a donation from a local resident. They turned over the DNA samples left over to Othram, a Texas-based genome sequencing lab that specializes in cold cases.
Typical consumer DNA test kits collect approximately 750 to 1000 nanograms of DNA in a sample. These samples are uploaded to public websites specializing in ancestry or health.
But crime scenes can only contain tens to hundreds of nanograms of DNA. And in this case, only 0.12 nanograms – or about 15 cells – were available for testing.
Using the ancestry databases, the researchers were able to identify the suspect’s cousin. Eventually, they matched DNA to Darren Roy Marchand.
Marchand’s DNA from a previous murder in 1986 was still on record and was used to confirm the match.
He was never convicted and committed suicide in 1995.
The genomic technology used to solve the case is the same one used to catch the infamous Golden State Killer in 2018.
“It was an important step,” Othram chief executive David Mittelman told the BBC.
“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.”
The company is currently working on cases dating back to 1881.