Recent advances in forensic science, including a powerful computer program able to reconstruct degraded D.N.A., allowed law enforcement officials in Utah this week to close a 52-year-old cold case and attribute the 1974 murder of a teenage girl to Ted Bundy, the serial killer.
Scientists at the Utah Bureau of Forensic Services linked Mr. Bundy, one of the nation’s most prolific and notorious spree killers, to the 1974 murder of Melissa Ann Smith. It was the second decades-old murder in the state attributed to Mr. Bundy this year. In April, investigators in Utah County determined that he had also murdered Laura Ann Aime.
Both were 17.
The body of Ms. Smith was found a few weeks before that of Ms. Aime. Now, their cases have been solved months apart, after the DNA found at one crime scene became instrumental in solving the other’s murder.
A key connection between the victims
Before his execution in 1989, Mr. Bundy admitted to killing Ms. Aime. But it was not until this year that sophisticated new technology existed to definitively connect him to her murder.
That technology not only closed the Aime case, but gave investigators new evidence with which to re-examine the Smith case.
“That Laura Aime case was what was key to solving the Melissa Smith case,” said Heather Mills, a forensic scientist at the Utah Bureau of Forensic Services.
Forensic scientists were able to connect the cases to each other and Mr. Bundy using a widely-available technology called STR genotyping as well as an innovative software known as STRmix.
STR stands for “short tandem repeat,” repeating blocks of genetic code found at certain locations throughout our DNA. Those locations have names such as CSF1PO, and D8S1179. Each person has STRs of different lengths across the genome, so if two samples have repeating code of identical length at many different places, they are likely to have come from the same person.
“What we’re looking at here are regions that can be distinguished from each other, not on the basis of their sequence, necessarily, but rather on the basis of their length,” said Dan E. Krane, a bioinformatics expert at Wright State University in Dayton, Ohio.
A ‘star’ comes to Utah
In 2011, the Florida Department of Law Enforcement uploaded Mr. Bundy’s DNA to CODIS, the nationwide forensic database, after a vial of his blood was found in a Florida courthouse.
Twelve years later, investigators in Utah ran a degraded sample of DNA found at Ms. Aime’s crime scene and ran it through STRmix, a software program that performs a type of analysis called probabilistic genotyping.
Developed by scientists in New Zealand, STRmix, pronounced “star mix,” separates and identifies multiple sources of DNA found in a single sample. This can be especially useful if the DNA of several people are mixed at a crime scene. The software uses modeling to build genetic profiles and gives a statistical readout about the likelihood of a match.
“If two people were wearing the same T-shirt, you might think that that’s unusual or it could still be coincidence,” Shoumita Dasgupta, a biomedical geneticist at Boston University, said of how STRmix works. “However, if two people were wearing the same T-shirt, pants, socks, shoes, watch, necklace and glasses, then coincidence is starting to become less likely of an explanation.”
After identifying a usable piece of DNA through STRmix, investigators ran it through the CODIS database. There was a match.
The results, Ms. Mills said, left little doubt that the DNA found on Ms. Aime belonged to Mr. Bundy.
Clues in a degraded sample
The case of Ms. Smith presented a different challenge. “We had evidence from Melissa Smith, but it was Y-STR evidence,” Ms. Mills explained.
That Y refers to the Y chromosome, which meant that investigators knew it came from a male, but determining from whom would be more difficult.
“Y-STR testing can be really valuable to just target in on male-specific DNA,” Ms. Mills said. “It’s really helpful when you have low-level or degraded samples where you might have a lot of human DNA, but just this very small amount of male DNA,” she added.
That turned out to be the case when it came to analyzing genetic material from the Smith murder.
Y-STR testing looks for exactly the same type of repeating blocks as autosomal STR testing, only it is confined to the Y chromosome, making it a valuable tool in sexual assault cases.
There was, however, a hitch. The Ted Bundy DNA in the federal database was not going to be helpful this time around. “We don’t know what his Y-STR profile is, so we can have evidence, but we don’t have anything to compare it to,” Ms. Mills said of the predicament she and her colleagues in the forensic lab faced.
But investigators already knew that Mr. Bundy was the killer of Ms. Aime from their earlier analysis. “We know he’s the male in that sample,” Ms. Mills said. Y-STR testing confirmed that Ms. Smith was, like Ms. Aime, a victim of Mr. Bundy.
Ms. Smith said it was gratifying to see new technology revive old evidence.
“That’s why we keep working cold cases,” she said.
The post The New DNA Technology That Linked Ted Bundy to a 52-Year-Old Cold Case appeared first on New York Times.
