DNA Evidence Links Suspect to Last Boston Strangler Victim

New DNA technology officially connects suspect Albert DeSalvo to 1964 murder victim Mary Sullivan.
15:12 | 07/11/13

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Transcript for DNA Evidence Links Suspect to Last Boston Strangler Victim
This is a special report from ABC. A letter when anti Hernandez in New York for this ABC news. Digital special report infamous cold case is heating up this morning. And Boston today authorities are set to reveal a quote major development. -- more than forty year -- hunt for the Boston strangler let's listen. Oakley. Right to my left him behind me while Boston Police Commissioner Ed Davis. Assistant district attorney pat Hagan first assistant district attorney Suffolk County. -- -- chief Daniel -- -- Assistant attorney general John Vernon and John -- -- dressed head of the criminal bureau. And nowhere is will Billy do get up here. -- Much -- such as detective well William Dugan who heads the rule -- the Boston Police. Cold case squad. And Don -- would like -- to please come up as well. -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- That's assembled team here today we announce a major development in the investigation into the homicide of nineteen year old Mary Sullivan. Almost fifty years ago. Mary Sullivan was raped and murdered and her body was desecrated in the bedroom of her Chal street apartment some time on the -- -- Of January 4 1964. Mary was as I mentioned nineteen years old. A sister a daughter a friend to so many. It was the last of eleven murders that would be attributed to the confessed Boston strangler. Albert. Henry to sellable. For almost five decades the only link between Albert Desalvo and Mary Sullivan's -- -- was his confession. That confession has been the subject of skepticism. And controversy from almost the moment it was given. It was not admissible in court. And -- to salvo was sentenced to life in prison for a series of non fatal sexual assaults. And not the strangling his. Not the strangler homicides. There was no forensic evidence to link Albert to sellable to Mary -- -- until today. Advances in the sensitivity of DNA testing have allowed us to make a familial match. Between biological evidence recovered from the crime scene and a suspect. In Mary -- -- that suspect is Albert to sell. Yesterday a Suffolk Superior Court Judge authorized the exhumation. Of the sell most remains but confirmatory testing. That we expect will prove to sell bulls guilt once and overall. I want to make clear that these developments be -- only on Mary Sullivan's murder. They don't apply to the other ten homicides popularly attributed to the Boston strangler. Even among experts and -- -- officials there is disagreement to this day about whether they were in fact committed by the same person. At this point in time. Fifty years removed from those deaths and without the biological evidence that we have -- the Sullivan case that's a question that we cannot answer. But these developments give us a glimmer of hope that they can one day be finality if not accountability. For the families of the ten of the women merited -- cruelly in Boston and Cambridge Lawrence -- And Salem between 1962 in 1963. I'll briefly summarize the evidentiary developments that bring us to this point today. DNA evidence was on -- off in the 1960s. But even then investigators believed that the killer had left biological evidence at the crime scene. Specifically. They recovered seminal -- from Mary Sullivan's body in a blanket on which her body was found. In the late 1990s. Boston Police criminalist attempted to extract a DNA profile from the stains on the blanket. At that point the crime lab was unable to extract DNA that was useful for comparison. Another round of testing took place in 2000 and in 2001. When the samples taken from Mary Sullivan's body at the time of her autopsy. Were tested. Again efforts to extract. A usable DNA profile. Was unsuccessful. The nature of these tests was such that each attempt to extract DNA consumed the entire sample. Meaning that it would be unavailable for further testing in the future. And for that very reason Don Hayes the director of the Boston Police crime laboratory all added that all further testing be halted immediately. Today we can say beyond any doubt that -- showed tremendous foresight. That decision meant that the remaining evidence would be stored -- the laboratory conditions. Until -- technology advanced and the chances locked within could be reached. Last year after a nationally recognized laboratory reported success. In obtaining DNA profiles from decades old samples the Boston Police crime lab notified investigators in the police commissioner. That renewed testing using the latest techniques. Could likely succeed where early attempts had failed. So last fall. The slides from miss Mary Sullivan's body. And the cuttings taken from the blanket. -- sent to cellmark and bode technology laboratories to highly respected. Independent laboratories. In unbeknownst to one another separate technicians at these two outstanding laboratories were able to develop. DNA profiles from the samples we sent them. I want to be clear on this point the evidence in this case never changed. But the ability that scientific ability to use that evidence has surpassed every -- And expectation. Of investigators who were first -- -- to the case. The stains from the blanket cuttings contain the unique genetic profile of an unknown male. The samples recovered from Mary Sullivan's body contained a mixture of two genetic profiles. One belonging to Mary herself. The other belonging to the same. Unidentified. Male whose DNA was extracted from the blanket. Given the facts and circumstances of this case. There can be no doubt that the male DNA. Belongs to the individual who merited and raped Mary Sullivan. These results are unprecedented in the history of this case. For the first time ever -- Forstmann has a piece of evidence to test against a suspect. Because he admitted to killing Mary Sullivan. Because he described this attack indeed tail to his attorney. -- to investigators. And because certain details of the crime similar to sexual assaults for which he was convicted and sentenced to life in prison. We started with Albert to salvo as the lead suspect. Through late last year and the -- a -- of this spring homicide detectives assigned to the Boston Police cold case squad. Along with Suffolk County prosecutors and prosecutors from attorney general Coke please office. Undertook an exhaustive search for any surviving evidence that might via the salvos DNA for comparison. They worked with the department of correction which had. Custody of Albert to -- -- from his 1967. Convictions. Until a time of his murder in prison. They work -- the state police and the Norfolk County district attorney's office which investigated. And prosecuted his 1973. Homicide. Pitchers -- When he was in Walpole state prison. They worked with the office of the chief medical exam which consolidated county based medical examiner system decades after. This Noble's body was autopsy all without success. They obtained a pair of letters that the sellable it sent to the -- and prison officials. And tried to extract from the glue on the envelopes. -- DNA profile again those efforts were unsuccessful. But among the most recent advances in DNA testing technology is the comparison of Y chromosomes. Which -- passed down. Almost unchanged. From father to son. Male descendants of the same father. She immediately identical Y chromosomes. Which can be competed through testing of biological material. Bearing this in mind in having exhausted every other avenue of inquiry. Boston Police retrieved a water bottle that one of Albert -- doubles nephews drank from and discarded. That -- was sent to cellmark laboratory. Where technicians once again were able to develop a DNA profile. The Y chromosome. From that profile was a familial match with the Y chromosome. From the sample taken. From Mary Sullivan's killer. That match implicates Albert to -- -- and excludes 99.9. Percent of others in the male population. This is good evidence strong evidence and reliable evidence. But it is not sufficient to close the case with absolute certainty. Many of you have covered what we call code -- -- cases. In which an unknown suspect is identified. When DNA from a crime scene matches that of -- known offender in the combined DNA index system database. Even in those cases when we get an exact match. Between crime scene evidence -- distort sample we still take the additional step. Of getting another sample directly from the defendant to confirm the match and this case is no different. To confirm the results that we have obtained thus far. We need a sample that can be established as Albert to sell most and that. Has to be maintained with a clear chain of custody under the stringent controls we demand in all homicide investigations. Towards that -- Suffolk prosecutors. Prosecutors from the attorney general's office and the Boston Police met with a Superior Court Judge yesterday. And obtained a search warrant. Authorizing the exhumation Albert cell walls remains -- author -- the testing. As they stated -- The exact number of homicides. Attributable to the Boston strangler remains controversial. We don't claim. With certainty that Albert to -- -- is the suspect in each of them. But we do believe that we stand on the threshold of -- of unprecedented certainty regarding Mary Sullivan's -- Finally. All bull this is a historic moment for the large -- agencies involved I want to recognize the civilians. Also involved. And who most directly affects. First and foremost -- die Ian dialogue and Casey Sherman Mary Sullivan's sister and nephew respectively. In many ways they kept this case alive through the decades through their perseverance. -- their commitment to finding the truth. I also want to acknowledge that the sellable family who did nothing wrong. But who found themselves in the shadow of accusations. That could never be fully proven or discounted. Police and prosecutors met with representatives of the families today to explain our findings in next steps. It was difficult in some ways. But I hope it sets the stage for closure that has eluded them. For more than twice as long as Mary Sullivan's. Lived on this earth now like to introduce Attorney General Martha Coakley. We've been listening to a news conference by Boston authorities regarding a key development. In the Boston strangler case DNA evidence has now conclusively linked. The last crime believed committed by the Boston strangler to the man. Who was originally believed to have been guilty but never proven so we're gonna bring -- caricature -- now. To recap a little bit of what we have heard Aaron really interesting -- here. Essentially the last victim Mary Sullivan was believed to have been raped and murdered. By Albert Desalvo but until today there was never any physical evidence linking it to. And here -- fifty years after that rape and murder. What prosecutors in Boston now believed to be definitive evidence. DNA all these years later and they are prepared now to exhume the body of Albert Desalvo in order to make that proves. Certain it is really an extraordinary event. In a case that is one of Boston's most notorious indeed maybe one of the most notorious. Crime scene crimes he's ever and and serial killers after the Boston strangler. Responsible for roughly a dozen murders around Boston between 1962. And 1964. Albert Desalvo is you heard the prosecutor say. Confessed but. It was never allowed in to court so he was sentenced on lesser crimes he died in 1973. And now they're ready to resume his body. Now that's Daryn as you -- it happened fifty years and they took some pains to explain why he's taken this long. You get a DNA link tell us about that. Well finally DNA testing is due to the point where it's sensitive enough to actually get some -- New and an updated DNA technology to identify. 9/11 victims of this technology is always evolving and it's getting ever more sensitive and it's finally to the point now. Where they can take a sample off saves you heard the prosecutor here. A water bottle and then compare -- with with other samples and finally exhumed the body of Albert -- to be sure. All right and that's certainly they did right now that the -- only linking this particular case and -- disagreement over the here -- whether all of these so called off his back victims. For the victims of this same person but it certainly in this case Wednesday -- about -- they believe they -- going to be able to finally. Close the case ABC's -- -- thank you so much for joining us this is an ABC news digital special report -- Hernandez in New York. This has been a special group. Report from me.

This transcript has been automatically generated and may not be 100% accurate.

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