This is part of an ongoing series from the MassLive Unsolved Case Files, a look at families of victims and the investigators who continue to dig for answers.

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The Middlesex District Attorney used genealogy websites, including Ancestry.com, to track down the brother of the man who killed 23-year-old Jane Britton, closing a nearly 50-year-old case.

Britton, who was described as a smart and funny Harvard graduate student, was found murdered in her bed in her Cambridge apartment in January 1969. Though the public clamored for answers following her death - which became a national news story - police never identified a suspect or made an arrest.

At a press conference Tuesday that changed. Middlesex District Attorney Marian Ryan for the first time identified Michael Sumpter, a serial rapist who died of cancer in 2001 as the killer. The mystery is over, Ryan declared.

In 2017 Ryan's office received several requests for Britton's file to be made public.

"Although prosecutors continued to hold out hope that there might be a DNA match to the partial profile taken from the scene that might identify the person who had killed Jane Britton, the case seemed to have hit a dead end," Ryan's office wrote in a news release.

A team of "experienced investigators" began to review the file and tried to find any additional leads that could be followed, particularly with advances in forensic DNA technology, Ryan's office said.

Investigators decided to perform additional DNA tests on the remaining evidence samples. In October 2017 the Massachusetts State Police Crime Lab found a male profile that matched the DNA samples on file. In July 2018, the State Police told investigators there was a match between the evidence sample and Michael Sumpter's file.

Sumpter, who is dead, has been tied to five sexual assaults, including three that ended in murder. He had been convicted of raping a woman in her Boston apartment in 1975.

In 2010, his DNA matched samples connected to the 1972 murder and rape of 23-year-old Ellen Rutchick in her Beacon Street apartment in Boston. In 2012, he was tied to the 1973 rape and murder of Mary Lee McClain in her Mount Vernon Street apartment, also in Boston.

Ryan said Sumpter did not know his victims, including Britton.

Using genealogy websites, including Ancestry.com, Massachusetts Police Sgt. Peter Sennott found Sumpter's brother. He went to his home and collected a fresh DNA sample.

"Testing on this sample excluded 99.92% of the male population as a contributor of the DNA and confirmed that Michael Sumpter's profile matched both the original soft hit and the Y-STR profile," Ryan's office said.

The use of genealogy sites in police work became mainstream in April when investigators in California arrested the so-called Golden State Killer. Joseph James DeAngelo, 72, was arrested and accused of committing more than 50 rapes and 12 murders over decades, according to report from the New York Times.

The emergence of DNA testing websites - like 23andMe and others - that gather genetic profiles from saliva sent to the company by customers through the mail have expanded the available genetic data for police.

One service, GEDmatch, said in a statement in April that law enforcement used its database to find DeAngelo. Officers found distant relatives of his, and traced their DNA to his front door, according to the Times.

GEDmatch said in the statement that it warned users their genetic information could be used for other purposes.

"If you are concerned about non-geneatological uses of your DNA, you should not upload your DNA to the database and/or you should remove DNA that has already been uploaded," the statement said, according to the Times.