Albert DeSalvo

(CBS/AP) BOSTON - DNA evidence has definitively linked Albert DeSalvo to the death of Mary Sullivan, a woman believed to be the Boston Strangler's last victim, authorities announced Friday.

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"Specifically, DNA specialists calculated the odds that a white male other than DeSalvo contributed the crime scene evidence at one in 220 billion," Suffolk County District Attorney Dan Conley, Attorney General Martha Coakley, and Boston Police Commissioner Ed Davis said in a joint statement Friday.

Investigators exhumed DeSalvo's remains for DNA testing last Friday after new evidence surfaced in the case.

The breakthrough happened after scientific advances that authorities said only became possible recently. Police secretly followed DeSalvo's nephew to collect DNA from a discarded water bottle to help make the connection.

DeSalvo admitting killing Sullivan in January 1964 and 10 other women in the Boston area between 1962 and 1964 in a series of slayings that became known as the Boston Strangler case. But he recanted in 1973 before dying in prison, where he was serving a life sentence for other crimes.

Sullivan grew up on Cape Cod before moving to Boston when she was 19. A few days later, she was dead -- raped and strangled in her new Beacon Hill apartment.

"We now have an unprecedented level of certainty that Albert DeSalvo raped and murdered Mary Sullivan," Conley said Friday.

"We now have to look very closely at the possibility that he also committed at least some of the other sexual homicides to which he confessed. Questions that Mary's family asked for almost 50 years have finally been answered. They, and the families of all homicide victims, should know that we will never stop working to find justice, accountability, and closure on their behalf."

Sullivan's nephew, Casey Sherman, spent much of his adult life searching for answers in the case and even wrote a book about it. Sherman had once joined with the DeSalvo family in believing that Albert DeSalvo wasn't his aunt's killer.

He said Friday that he thinks there will always be unanswered questions related to the Strangler case, but when it comes to his loved one's slaying, his family finally has a sense of closure.

"He's the killer of my aunt, which is all this has been about for me," Sherman said.

Conley has said the new evidence applies only to Sullivan's homicide and not to the other Strangler-linked killings.

He said some law enforcement officials still disagree about whether one person committed all 11 slayings.