Those fortunate enough to have a head of hair generally leave 50 to 100 strands behind on any given day. Those hairs are hardy, capable of withstanding years or even centuries of rain, heat and wind.

The trouble for detectives is that unless it contains a root, which only a tiny percentage do, there’s no hope of generating a DNA profile. Until now.

Ed Green, a paleogeneticist at the University of California, Santa Cruz, known for his work on the Neanderthal genome, has developed a technique that makes it possible to recover and sequence DNA from hair without the root.

During the past 18 months, he has been quietly cooperating with law enforcement agencies to extract genetic profiles from the hairs of killers and victims in unsolved crimes.

“It was kind of written in stone that you can’t do it, and now he’s doing it,” said Deputy Pete Headley of the San Bernardino County Sheriff’s Department in California.

Justin Loe, the chief executive of Full Genomes, a genetics services company, called the technique “a game-changer.”

“Criminals think of wearing gloves or wiping down blood,” he said, “but fewer think to shave their head.”

The hair sent to Green is usually hand-delivered by law enforcement to his lab. Some packages contain a single lock, shorter than a thumbnail; others hold long clumps. Some belong to serial killers who have evaded detectives for decades; others to victims.

Once the DNA is extracted it is kept in a liquid, in a rack just across the room from the cold storage refrigerator containing mammoth bones, dodo birds and an extinct American cheetah, among other treasures.

In 2005, Green was part of a team at the Max Planck Institute, which developed an advanced genetic sequencing technology to read DNA extracted from fossilized bones. In 2010, he was involved in sequencing the Neanderthal genome from a bone shards at least 38,000 years old.

Carlos Bustamante, a geneticist at Stanford University, credited Green with creating a series of technologies that enabled extracting more from less. “We went from zero reliable ancient genomes to thousands and thousands of ancient genomes,” he said.

Hair was not Green’s focus until genetic genealogist Barbara Rae-Venter called him. “For really old things it’s hard to find hair,” he said.

Fine-tuning the process took about a year. It used to be that DNA could only solve a case if it matched someone in a criminal database or an existing suspect. But with the rise of genetic genealogy, which enables identifying DNA through relatives in genealogy databases, DNA’s value to investigators has skyrocketed.

Nearly half the time, genetic genealogists will tell you, they can turn a DNA profile into a suspect’s name.

Green submitted a paper to scientific journal. Once published, he is aware that the technique could be used for trivial crimes, corporate espionage or harassment and said “there need to be rules or how that power is wielded.”

Suzanna Ryan, a forensic consultant and lab director who recently forwarded a case to Green involving a woman’s embalmed head, said there are 200,000 to 250,000 U.S. cold cases and even if hair was collected in just 10%, that’s 20,000 cases that could benefit.

But hurdles remain. Forensic labs are not set up to implement it and it is expensive. Each hair costs several thousand dollars to sequence.