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On Jan. 4, 1964, Mary Sullivan was strangled and raped in her Boston apartment. Among the evidence collected by police was seminal fluid from her body and from a blanket.

DNA testing did not exist then, but the Boston police crime lab held on to the evidence in hopes it might one day lead to the killer of the 19-year-old who had moved from her Cape Cod home to Boston days before her death.

On Thursday, authorities in Boston said the nearly 50-year-old evidence had produced a DNA match that links Albert DeSalvo, long suspected as the Boston Strangler responsible for 11 slayings, to Sullivan’s death. She has long been considered the strangler’s last victim.

Breakthroughs in DNA testing found a “familial match” between the killer’s seminal fluid and a living nephew of DeSalvo, who was stabbed to death in prison in 1973. A fugitive-squad cop from the Boston Police Department followed the nephew and recovered a discarded water bottle containing his DNA, authorities said at a news conference in Boston.

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“We got a hit,” Boston Police Commissioner Edward Davis said of the DNA testing.

Suffolk County District Attorney Daniel Conley said the DNA match ruled out 99.99 percent of all other males. “There was no forensic evidence to link Albert DeSalvo to Mary Sullivan’s murder until today,” he said.

Although DeSalvo, an Army veteran with a wife and children, had confessed to the Strangler killings, he was never charged or convicted in connection with the slayings.

The killings terrorized the city and achieved cult status with “The Boston Strangler” movie starring Tony Curtis as DeSalvo.

DeSalvo was serving a life sentence for unrelated armed robberies and sexual assaults and was stabbed to death in the state’s maximum-security prison in Walpole in 1973, but not before he recanted his confession. Doubts about the confession persisted.

Conley said he expects a match to DNA from DeSalvo’s remains after they are exhumed this week under a judge’s order. Authorities stressed that the DNA evidence applies only to Sullivan among the women, age 19 to 85, who were raped and slain in the Boston area between 1962 and 1964.

“We are aware of no other DNA evidence that has survived from any of the other 10 murders we have been looking at,” said Massachusetts Attorney General Martha Coakley.

Among those who fought to clear DeSalvo’s name was Sullivan’s nephew, Casey Sherman. But at the news conference, Sherman said the new evidence “provides an incredible amount of closure” for the Sullivan and DeSalvo families. “I only go where the evidence leads,” he said.

Police tried and failed several times over the years to obtain DeSalvo’s DNA. They even tried to extract DNA from saliva on envelopes he sent from prison, Conley said.

The Sullivan evidence was also tested over the years, but parts of the samples were destroyed each time. Boston Police Crime Lab director Donald Hayes decided several years ago to hold off on further testing to await advances in DNA testing and forensic technology.

Davis, the police commissioner, said Hayes told him in 2006 that the lab had retained and stored six samples from Sullivan’s body and the blanket. They remained on slides in storage until last year, when the National Institute of Justice awarded the department a $300,000 grant for cold-case investigations.

The Sullivan slides were sent separately to two independent laboratories for testing.

Ultimately, one lab was able to extract identifiable DNA from the seminal fluid. But police still needed a DNA sample from a male DeSalvo relative; Y chromosomes are passed directly from father to son.

The fugitive-squad officer, an expert in surveillance, was dispatched to follow DeSalvo’s male relatives. Authorities did not directly approach the family to request a sample for fear that they would not cooperate, Conley said.

An attorney for the DeSalvo family, Elaine Whitfield Sharp, called the DNA evidence strong but not definitive. She said the family had offered to provide DNA in the past and was angry to learn of the secret surveillance, which Sharp called an “unwarranted invasion of privacy.”

Material from The Associated Press is included in this report.

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