Here's how a napkin and a public DNA website lead to a 32-year-old murder case being solved

If there's one thing that can devastate a community, it's an open murder case. If someone has been killed in your neighbourhood, and there are no arrests afterwards, you never quite feel safe there again. It's a sad fact that, despite the best intentions of modern police precincts, there are some homicides that will never be solved. Any good detective worth his salt will tell you that, the colder a case gets, the harder it is to close. Every day, week and month that passes means that new leads are less likely, that crucial evidence will be lost forever, and that witnesses' memories will become cloudy and vague.

But the good news is that forensic technology is advancing all the time, and as such, more and more criminals, some of whom committed their gruesome felonies decades ago, are finally being brought to justice. Today, DNA analysis is so precise, that a tiny fibre or droplet of blood is enough to convict someone. This week, all it took was a napkin and a genealogical website to finally solve a murder that took place more than 32 years ago.

In March of 1986, 12-year-old Michella Welch was found raped and murdered in a Washington state park. She was babysitting her two younger sisters and had left them briefly to travel back home via bike to make them sandwiches. She must have returned to the park at some point, because her bike and the sandwiches were later found at the scene, but Michella herself was missing.

Police dogs later located her body in a ravine just before 11pm. There was little evidence to go on, and investigators were faced with the possibility of a stone-cold whodunnit; the police diligently developed a DNA profile from the recovered evidence, but couldn't find a match in state and national databases.

Six months later, another 13-year-old, Jennifer Bastian, was found raped and strangled on a trail in Tacoma, which led the police to theorise that it was the same killer, since the modus operandi was almost identical. The case stagnated, and there wasn't a break until 2013. A new piece of DNA evidence found near Bastian's body revealed that there were actually two separate killers.

In 2016, the county prosecutor's hired a "genealogist" working for Parabon NanoLabs in Virginia, to build a family tree using public genealogy databases and DNA testing kits from companies like 23andMe and Ancestry.com, with DNA collected from the scene of Welch's death. After pairing it with relevant data, they found that the only possible matches were retired nurse Gary Hartman, and his younger brother. Both had lived near to Welch at the time of her death.

However, it was useless as evidence until they authorities gathered a sample of Hartman's DNA. On June 5, 2016, one of the investigators tailed Hartman to a diner and stole a napkin he'd used to wipe his mouth with. Once they'd determined that the DNA matched, the police arrested Hartman while he was driving. On Friday he was charged with first-degree murder and first-degree rape, and he has been jailed on a $5 million (£3.7 million) bail.

Commenting on the case, Pierce County Prosecutor Mark Lindquist stated: "DNA technology is rapidly advancing. If you’re a criminal who left DNA at a crime scene, you might as well turn yourself in now. We will eventually catch you."

This dramatic turn of events has come just a few weeks after police used genealogical forensics to finally catch the Golden State Killer, aka retired cop Joseph James DeAngelo, who killed and raped over 50 women in the Sacramento area of California in the 1970s. These cases prove that continuous investigations can yield results, and justice can finally be won for the victims and their families.