Hairs Found on Victims' Bodies Were Crucial Evidence Against Long Island Serial Killer Suspect: Prosecutor

Rex Heuermann, the man police allege to be the Long Island Serial Killer, allegedly meticulously covered his tracks over the years, using burner phones to contact his victims, fake online identities to track their families, and waiting for his wife and kids to go out of town before committing his next crime.

But the 59-year-old architect accused of killing at least three sex workers more than a decade ago made some crucial mistakes, Suffolk County District Attorney Ray Tierney claims to PEOPLE.

Tierney says authorities were able to narrow in on Heuermann as their primary suspect using cell tower data, a witness’s description of his Chevrolet Avalanche, and eventually DNA from five hairs found on three of the victims.

According to a bail application obtained by PEOPLE, prosecutors say one hair was found on Maureen Brainard-Barnes, two were found on Megan Waterman and another piece of hair was found on Amber Costello. But at the time the three women’s remains were discovered in New York’s Gilgo Beach area in December 2010, the hairs “were not suitable” for nuclear, or traditional, DNA testing, Tierney says.

But luckily, investigators collected the evidence anyways, Tierney says.

“Then as the technology progressed, there's this thing called mitochondrial DNA [and]  they became more suitable for that,” the district attorney says.

A mitochondrial DNA test can trace a person’s maternal ancestry, but it needs a sample to be compared to. “So the Suffolk County PD and the FBI surveilled” Heuermann, Tierney says, obtaining DNA samples from him and his wife off of objects they discarded.

“Now, we go back and we perform that analysis. Two out of the three hairs on Megan Waterman. One, the mitochondrial DNA profile obtained from that hair matches the defendant. One other DNA profile on that hair matches his wife, such that over 99 percent of the rest of the population can be excluded,” he claimes.

Heuermann also says the hair found on Amber Costello “matched the wife,” as well. 

“We know that hair – his hair and his wife's hair – were found on the girl,” Tierney says. “So that could mean one of two things. There's transfer, meaning if I come in contact with my wife in the morning and one of her hairs gets on my clothes and then I come in contact with someone else, that hair could fall on them. That's called transfer. Or if someone comes to my house or comes into my car that I share with my wife and they sit down and it goes directly onto them.”

Tierney says investigators are still looking into where the murders were committed.

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Authorities have alleged that Hueremann committed the murders while his wife and two kids, who all lived with him at his Massapequa Park, N.Y., home, were out of state.

“I think he lived this double life,” Tierney claims. “He used the anonymity of phones and computers and our modern life to shield himself or part of himself from the rest of society. He had the part of him that faced the public and the part of him that didn't. He was disciplined in trying to keep that hidden. Unfortunately for him, and fortunately for the rest of us, he wasn't successful.”

Heuermann's next court hearing is in early August, according to the district attorney.