In 1915, a team of U.S. archaeologists excavating the ancient Egyptian necropolis of Deir el-Bersha blasted into a hidden tomb. Inside, they were greeted by a mummy’s severed head perched on a cedar coffin.

The room, labeled Tomb 10A, was the final resting place for a governor named Djehutynakht and his wife. At some point during the couple’s 4,000-year slumber, grave robbers ransacked their burial chamber and then attempted to set the room on fire.

The archaeologists recovered painted coffins and wooden figurines and sent them to the Museum of Fine Arts, Boston, in 1921. Most of the collection stayed in storage until 2009 when the museum exhibited them.

The head became the star of the showcase, bringing viewers face to face with a mystery.

“We were never sure if it was his head or her head,” said curator Rita Freed.

The museum staff concluded only a DNA test would determine which was on display. But Egypt’s scorching climate rapidly degrades DNA.

To crack the case, the museum turned to the FBI.

The FBI had never before worked on a specimen so old. If its scientists could extract genetic material, they would add a powerful DNA collecting technique to their forensics arsenal and also unlock a new way of deciphering Egypt’s ancient past. “There was this belief that it was not possible to get DNA from ancient Egyptian remains,” said Odile Loreille, an FBI forensic scientist.

But in the journal Genes, Loreille and her colleagues reported that they had retrieved ancient DNA — and solved the mystery of the mummy’s identity.

As Freed prepared the exhibition in 2005, she reached out to Massachusetts General Hospital. Its CT scan revealed the head was missing cheek bones and part of its jaw hinge — features that may have potentially provided insight into the mummy’s sex.

The doctors and museum staff turned to the mummy’s molar. Teeth often act as genetic time capsules.

The first tooth they targeted would not budge, so Dr. Fabio Nunes switched. Sweating, he clamped down with dental forceps, gave it a few wiggles, then a few twists and “pop” — it was free. “My main concern was: Don’t drop it, don’t drop it, don’t drop it,” he said.

For several years, scientists tried fruitlessly to get DNA from the molar. Then the crown of the tooth went to Loreille at the FBI’s lab in Quantico, Va., in 2016. She had previously extracted genetic material from a 130,000-year-old cave bear, and worked on cases to identify a 2-year-old child who had drowned on the Titanic and two of the Romanov children.

In the clean lab, Loreille drilled into the tooth, collected a bit of powder and amplified the DNA. She plugged her data into software that analyzed the ratio of chromosomes. “When you have a female you have more reads on X. When you have a male you have X and Y,” she said. The program spit out “male.”

Loreille discovered the mummified head had belonged to Djehutynakht. In doing so, she helped establish that ancient Egyptian DNA could be extracted from mummies. “It’s one of the Holy Grails of ancient DNA to collect good data from Egyptian mummies,” said Pontus Skoglund, a geneticist in London who helped confirm the accuracy while at Harvard.

Loreille’s examination also showed that Djehutynakht’s DNA carried clues to another mystery. For centuries, scientists have debated the origins of the ancient Egyptians and how closely related they were to modern people living in North Africa. To the researchers’ surprise, the governor’s mitochondrial DNA indicated his ancestry on his mother’s side was Eurasian.

“No one will ever believe us,” Loreille recalled saying. “There’s a European haplogroup in an ancient mummy.”