Heuermann has not been charged in the death of Mack. But asked during a news conference after Thursday’s hearing if he was a suspect, District Attorney Ray Tierney replied: “That’s fair to say.”

Tierney also acknowledged that the “blueprint” document, which Heuermann had attempted to delete, was a “significant impetus” for the renewed search across Long Island in recent weeks. It was recovered in March from the more than 350 electronic devices seized from the suspect’s home.

Heuermann pleaded not guilty to killing Taylor and Costilla during the hearing and was ordered to be held without bail. His lawyer, Michael Brown, said outside court that Heuermann was “obviously in a bad place in terms of the new charges”.

Afterwards, Tierney said the additional charges provided “some small measure of closure” for the victims’ families.

Not the same killer

Since late 2010, police have been investigating the deaths of at least 10 people – mostly female sex workers – whose remains were discovered along an isolated highway not far from Gilgo Beach on Long Island’s south shore.

Those victims disappeared over a span of at least 14 years. Vexed detectives made only halting progress in identifying possible suspects. Investigators have long said it was likely that not all of the deaths were the work of the same killer. Some of the victims vanished in the mid-1990s. Investigators concluded that an 11th person who disappeared in 2010 from the barrier island community of Oak Beach had accidentally drowned.

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Heuermann, who lived across a bay from where the bodies were found, was arrested last July. Prosecutors said a new investigative taskforce used mobile phone location data and DNA samples to link the architect to some of the victims. He was charged with killing four of the women: Megan Waterman, Melissa Barthelemy, Amber Lynn Costello and Maureen Brainard-Barnes.

Investigators who extensively searched Heuermann’s home and dug up his yard last summer returned to the house last month and spent nearly a week searching it again. According to a lawyer for Heuermann’s wife, they focused their efforts mostly in the basement.

That followed a search in April of a wooded area in Manorville, about 65 kilometres east of Heuermann’s home, and in the Southampton hamlet of North Sea, where Costilla’s remains were discovered decades ago.

Tierney said the planning document was recovered in March, providing the impetus for the recent searches.

Prosecutors said they found a book in Heuermann’s possession by retired FBI agent John Douglas, The Cases That Haunt Us. They say the planning document referenced specific pages in another work by Douglas, Mind Hunter, that allude to the personality types of serial killers and profiles of those who use mutilation and sexual violence.

Jessica Taylor, 20, vanished in 2003 while working as an escort in New York City. Some of her remains were discovered in Manorville that year. Other remains were found during a 2011 search of the beach scrub by the side of Ocean Parkway, the road where the other Gilgo Beach victims were found.

Taylor’s mother, Elizabeth Baczkiel, was at the courthouse for Thursday’s hearing. She held up childhood photos of her daughter but didn’t speak to reporters. Her lawyer, Gloria Allred, read a statement from Baczkiel in which she described her daughter as “loving, compassionate and so funny”, and said she would have made a great mother.

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“My darling daughter, you will never be forgotten,” the statement said. “You will forever be in our hearts.”

Valerie Mack, 24, who had been working as an escort in Philadelphia, disappeared in 2000 and was last seen by her family in Port Republic, New Jersey, near Atlantic City. Some of her skeletal remains were discovered that year in the Manorville woods. More of her remains were found in 2011 during the search around Gilgo Beach.

Initially known as “Jane Doe No. 6”, Mack’s remains went unidentified until 2020 when genetic testing revealed her identity.

Costilla was 28 when she was killed and had lived in New York City.

‘Meaningful investigation’

A decade ago, Suffolk County prosecutors said publicly that they believed Costilla had been killed by John Bittrolff, an area carpenter who was convicted of murdering two other women whose bodies were found in the same part of Long Island.

But Bittrolff was never charged with Costilla’s death due to lack of evidence and has insisted he didn’t kill anyone.

“After today’s confirmation that John Bittrolff had nothing to do with the death of Sandra Costilla, I sincerely hope that the Gilgo Beach Task Force will conduct an actual, meaningful investigation into the murders of Rita Tangredi and Colleen McNamee to find their real killer,” his lawyer, Jon Manley, said on Thursday, referring to the two women Bittrolff was convicted of killing.

Michael Brown, Heuermann’s lawyer, said he planned to request the prosecution’s files on Bittrolff.

“Quite frankly, the police department and the district attorney’s office all had the finger pointed at Bittrolff for that murder,” he said.

AP