Should DNA Really Be Used To Crack Cold Cases?

Law enforcement agencies have started investigating unsolved crimes by combining DNA databases and family trees. But should ‘genetic genealogy’ really be used to crack cold cases?

- Jv Chamary

From 1976 to 1986, the residents of California were terrorised by a masked man who raped at least 48 women and murdered a dozen people. His carefully planned attacks suggested military training, but after three decades, the East Area Rapist – also known as the Golden State Killer – seemed to have got away with his crimes. The case went cold.

Then on 25 April 2018, law enforcement officials announced that they had arrested Joseph DeAngelo, a 72-year-old Navy veteran and former cop. Investigators explained that semen samples from crime scenes had been used to produce the perpetrator’s DNA profile and search an online database for potential relatives. The list of matches was then used to build a family tree that led to DeAngelo.

While catching killers using ‘genetic genealogy’ might sound like an obvious idea, it is by no means straightforward. “Humans are really similar genetically: if I compared my genome to yours, we’d be 99.99 per cent identical,” says Prof Graham Coop, a population geneticist at the University of California, Davis. “But there are positions in DNA which are variable between individuals.”

TESTING METHODS

Modern genetic tests read the letters of DNA at a selection of positions across the human genome to generate a profile of genetic variants. These single-letter differences represent DNA regions that often vary among people, called ‘single nucleotide polymorphisms’ or SNPs (pronounced ‘snips’).

Personal genomics companies like 23andMe and Ancestry offer ‘direct-to-consumer’ DNA tests that read about 700,000 SNPs. Those variants generate a profile that claim to reveal your family history, ethnic background and susceptibility to disease.