A massive murder investigation that involved more than 15,000 DNA samples to catch the killer of a 13-year-old Italian girl was awarded the “DNA Database Hit of the Year” by an influential lobbying firm.

The case that resulted in life imprisonment for the killer of Yara Gambirasio, who was killed in November 2010, involved a series of breakthroughs in pulling a DNA profile from a dead man’s postage stamp, then using Y-STR and mitochondrial profiles to determine the real parents of the murderer.

Massimo Bossetti, 46, still maintains his innocence from behind bars. But his DNA is a near-perfect match to the profile pulled from the pants of Gambirasio, whose body was found three months after she disappeared on her half-mile route home from the local gym.

The seven international judges of the annual award picked the Italian case from five finalists, which included runners-up from China, Austria and the U.S.

“I have never seen a case where so much effort was put into a finding a suspect through the use of DNA,” said Rock Harmon, a retired Alameda County, California prosecutor and DNA expert. “The men and women of the Italian Carabinieri and the Polizia di Stato should be commended for their tireless work to identify the person that matched the DNA left at the crime scene.”

The complex investigation started with DNA on the body, proceeded through thousands of voluntary test samples and involved years of genetic detective work.

Upon the discovery of the girl’s body in February 2011, investigators found the full DNA profile of the presumed killer—a man they dubbed Ignoto Uno (“Unknown One”). The local police then undertook the voluntary testing of people in the area—totaling a staggering 15,000 people.

That testing pulled up a partial match of a man in the area who had frequented a dancehall in the area, according to news accounts. The man’s DNA did not match the crime scene profile, but the genetic similarities indicated a close relative. The man’s father was one of 11 siblings—which led to a particular uncle, Giuseppe Guerinoni.

But Guerinoni had died in 1999. So his widow provided a piece of mail with a postage stamp he licked decades ago. A match of the Y chromosome indicated they were on the right track, and they confirmed the information with an exhumation of Guerinoni.

The presumed killer had to be a son of Guerinoni, a longtime bus driver in the area around Brembate di Sopra, they determined. But Guerinoni’s children didn’t match.

Guerinoni, who was known as a ladies’ man, was suspected of having illegitimate children in the area. So authorities began working on a list of women he may have had an affair with.

The authorities conducted another massive voluntary DNA round of testing, this time involving 600 women. They came up with a perfect match for the killer’s mother: a woman who had been married for decades and had two sons and a daughter. The police set up a breathalyzer checkpoint to get the eldest son’s DNA. The son, Bossetti, turned out to be a perfect match for the presumed killer’s DNA profile on the girl’s pants.

That match led to a conviction for Bossetti, who was sentenced in July 2016 to life in prison.

The “Database Hit of the Year” is awarded by Gordon Thomas Honeywell Government Affairs.

“The DNA Hit of the Year Award is designed to bring increased awareness to the incredible power of forensic DNA databases to solve crime and provide closure to victims and their families,” said Tim Schellberg, the president of the firm. “It also recognizes the dedication of investigators and forensic scientists throughout the world who use DNA databases to pursue justice.”