DNA finally nails the notorious Boston Strangler

Between 1962 and 1964, the Boston Strangler claimed the lives of at least 11 women. Now, half a century later, DNA evidence has confirmed that the chief suspect, Albert DeSalvo, raped and murdered one of those victims, 19-year-old Mary Sullivan.

DeSalvo confessed to killing Sullivan and about a dozen other women, but later recanted that confession and was never convicted. He was killed in prison in 1973 while serving time for other crimes.

In a bid to solve the mystery, the Boston Police Crime Lab dug up DeSalvo's corpse and removed three teeth and a section of bone from his left arm. The DNA matched degraded samples of DNA that were from the crime scene, which were analysed using sensitive techniques that have only become available in recent years.

Late in 2012, male DNA was extracted from Mary Sullivan's remains and the blanket on which her body was found by two forensics labs ? Bode Technology in Lorton, Virginia, and Orchid Cellmark in Dallas, Texas. Both agencies use advanced techniques to derive profiles from degraded DNA.

While both labs found the same profile, investigators found no match for it in the FBI's CODIS database of previous offender's DNA profiles.

Lucky break

The next task was to obtain DNA from DeSalvo, which meant exhuming his body. "To get an exhumation they needed probable cause," says Bruce Budowle at the University of North Texas in Denton, formerly the FBI's leading specialist on forensic DNA profiling.

That legal requirement was met after matching the unknown DNA profile with that of DeSalvo's fraternal nephew, using a water bottle that he had drunk out of, scavenged by the Boston Police. Based on genetic markers on the Y chromosome, which is passed intact down the male line, investigators were able to implicate DeSalvo and exclude 99.9 per cent of the male population. The implication is that the DeSalvo males' must have a rare Y chromosome type ? a lucky break for investigators.

When DeSalvo's DNA was tested by Orchid Cellmark, it matched the crime-scene DNA. In a press conference in Boston on Friday, the director of the Boston Police Crime Lab, Donald Haynes, explained the level of confidence in the match: "You'd have to search four planet Earths to find one person with that profile, and Albert DeSalvo had that profile."

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