DNA tests confirm that the man who once claimed to be the Boston Strangler did kill the woman believed to be the serial killer's last victim and was likely responsible for the deaths of the other victims, authorities have said.

Albert DeSalvo admitted to killing Mary Sullivan and 10 other women in the Boston area between 1962 and 1964 but later recanted. He was later killed in prison.

Eleven Boston-area women between the ages of 19 and 67 were sexually assaulted and killed between 1962 and 1964, crimes that terrorized the region and grabbed national headlines.

The DNA finding "leaves no doubt that Albert DeSalvo was responsible for the brutal murder of Mary Sullivan" and it was "most likely" that he also was the Boston Strangler, Massachusetts Attorney General Martha Coakley said.

Authorities said recently that new technology allowed them to test semen left at the crime scene of Sullivan's death using DNA from a living relative of DeSalvo's. That produced a match with DeSalvo that excluded 99.9 per cent of suspects, and was the first forensic evidence tying DeSalvo to the nearly 50-year-old case.

To confirm the match, investigators unearthed his remains a week ago and said yesterday that the odds that the semen belonged to a male other than DeSalvo were 1 in 220 billion.

"It's a great day. This is now full justice for my aunt, Mary Sullivan," said her nephew, Casey Sherman.

A lawyer for DeSalvo's family, Elaine Sharp, said last week that even a perfect DNA match wouldn't mean he killed Sullivan and suggested that someone else was present at the slaying. She said previous private testing on Sullivan's remains showed the presence of DNA from what appeared to be semen that wasn't a match to DeSalvo.

Police responded last week by saying the evidence used in private testing from Sullivan's exhumed remains was "very questionable."

Sharp also said in a statement that DeSalvo's brother and his nephew whom police secretly trailed to collect a family DNA sample from a discarded water bottle won't comment on the new DNA result because it hasn't been proven to be relevant to the question of whether DeSalvo raped and strangled Sullivan.

"There is no level of 'unprecedented certainty' as now claimed by the government," Sharp said.