Police Say Accused Long Island Serial Killer Rex Heuermann Allegedly Kept Track of His Victims' Families

New York authorities said Long Island Serial Killer suspect Rex Heuermann “compulsively” searched for photos of his victims and their family members.

At a press conference on Friday, Suffolk County District Attorney Ray Tierney said Heuermann, 59, used an online account to repeatedly view images of his alleged victims and their family.

“He was compulsively searching pictures of the victims, but not only pictures of the victims, pictures of their relatives, their sisters, their children, and he was trying to locate those individuals,” Tierney said.

Heuermann, an architect and married father of two, was charged Friday with three counts of first-degree murder and three counts of second-degree murder in the deaths of Melissa Barthelemy, Megan Waterman and Amber Costello.

He is also considered a prime suspect in the death of Maureen Brainard-Barnes.

All four women had worked as online escorts and had been missing between 2007 and 2010. Their bodies were found along a half-mile stretch of Ocean Parkway in Long Island, New York, in December 2010.

Heuermann was allegedly linked to the killings by burner phones used to rendezvous with the victims, as well as by a piece of his hair allegedly found at the bottom of a burlap bag used to wrap Waterman’s body.

He was also traced to a Chevrolet Avalanche that was registered to him that was seen at the time of Costello's disappearance.

"That individual was identified as a person who was between 6'4" and 6'6", a large man, thickly built, not necessarily overly muscular, but just a naturally big person with glasses, white and dark hair," Tierney said. "Also of significance was the fact that he was driving a dark-colored black first-generation Chevrolet Avalanche."

Authorities said investigators also found evidence that Heuermann was obsessed with the case and searched for articles about the task force that was formed to investigate the murders.

“In a 14-month period, he had over 200 searches pertaining to the Gilgo investigation,” Tierney said. “Not only was he looking at investigative insight, he was trying to figure out how is the task force using cell phones to try to figure out what’s happened. What are the developments with regard to the task force.”

The Gilgo Beach case, dubbed the “Long Island Serial Killer” case, traces back to the discovery of Costello, Barthelemy, Brainard-Barnes and Waterman in December 2010. Authorities eventually unearthed 10 sets of remains in the area.  

Brainard-Barnes, 25, disappeared first — in July 2007, from New York City — after checking out from a Super 8 motel.

Barthelemy, 24, was last seen walking away from her Bronx apartment in 2009.

Want to keep up with the latest crime coverage? Sign up for PEOPLE’s free True Crime newsletter for breaking crime news, ongoing trial coverage and details of intriguing unsolved cases.

Waterman disappeared from a Holiday Inn Express room she was sharing with her boyfriend Akeem Cruz in Hauppauge after she placed an ad on Craigslist on June 5, 2010.

Costello negotiated a $1,500 date with her alleged killer before she walked out of her Long Island home on Sept. 2, 2010.

Initially, authorities had been looking for Shannan Gilbert, another sex worker who escaped from a home and called 911. Gilbert was found one year later, and police believe her death was accidental.