Image source, Getty Images Image caption, Crime scene evidence is often not enough to identify suspects
Randy Gail Sperino was last seen alive on the evening of 9 November 1993, as she was getting into a pickup truck in Granite City, Illinois.
The 34-year-old's body was found hours later in a field nearby, the victim of blunt force trauma.
The identity of her killer was a mystery. DNA evidence found at the crime scene was tested against standard law enforcement databases, but no matches were found.
For three decades, investigators from the Madison County Sheriff's Office chased leads and interviewed hundreds of people as they attempted to identify the perpetrator.
The case looked like it would remain one of more than 250,000 unsolved homicides in the US.
Then, last year, detectives tried a fresh approach. They sent genetic evidence to Othram, a Houston-based company that uses DNA technology to help identify the perpetrators in cold and current crime cases.
The Madison County detectives had been inspired by investigative genetic genealogy techniques used to identify the Golden State Killer, Joseph James DeAngelo, back in 2018. In that case, an investigative team constructed a family tree to help identify the killer.
They were able to do so thanks to DNA data that relatives had provided to commercial databases, similar to consumer ancestry platforms.
Unlike traditional forensic DNA testing, which generally relies on a direct comparison between evidence and a known person, investigative genetic genealogy can identify distant genetic relatives of an unknown individual.
Othram set about applying this technique to track down Sperino's killer. While the killer's own DNA profile wasn't available, profiles submitted by his extended relatives allowed the company to identify a male family member.
"That lead broke the case open," said Captain Tim Lawrence of Madison County Sheriff's Office, which was responsible for investigating the crime.
It was a crucial clue that led the detectives to Albert "Buddy" Zigler, 70, who then confessed to the murder. He was charged in May this year.
Wes Sperino, Gail's son, said at a press conference: "I finally get closure and I finally know who did this."
Image source, Madison County Sheriff's Office Image caption, Albert Zigler was charged with murder in May
The technique that led detectives to Zigler is credited with revolutionising how forensic cases are solved.
It has been highly successful in helping solve cases involving unidentified human remains and identifying suspects in longstanding investigations.
Othram claims it has helped solve thousands of cases. The company's chief executive David Mittelman likens investigative genetic genealogy to a GPS system: "The DNA profile is the GPS signal and it says 'you belong here.' But to understand where 'here' is, you need a map."
Public records, obituaries, and census data build that map so Othram's scientists can establish how different family trees connect.
However, Mittelman is quick to point out that DNA technology can only go so far before "a cascade of investigative steps" are needed.
Image source, Othram Image caption, An Othram scientist prepares a bone for DNA extraction
DNA science isn't the only technology that are helping detectives solve cold cases.
One of the challenges facing detectives on major cases investigations like the hunt for Sperino's killer i…