Court documents released Friday detail what finally led police to the suspected killer of at least three of the Gilgo Beach victims.

Police say they were able to ping Rex Heuermann's location using billing records for burner phones he allegedly used to talk with the victims , including Melissa Barthelemy, Megan Waterman and Amber Costello, before they disappeared.

Rex Heuermann used two of the victims' phones after their deaths to check their voicemails and make taunting calls to their relatives, according to court documents.

Those calls were made in midtown Manhattan where Heuermann works.

LIVE BLOG: Updates on the case as they happen Investigators say another one of the victim's cellphones was last pinged near the suspect's home in Massapequa Park.

Neighbors were shocked to hear that the calls were made so close to their homes. “That just takes it to a whole another level,” says Jenna Datlo. “I mean, that’s just monstrous."

Heuermann is also the suspect in the death of a fourth woman, Maureen Brainard Barnes.

Authorities say Heuermann used a device to contact Brainard Barnes 16 different times in July 2007.

At one point, authorities believe the defendant used one of the cell phones from Barthelemy after she went missing to call the victim’s relative.

Cell phone records show that Heuermann made many of the calls to his alleged victims near his residence in Massapequa Park. He would travel to and from his job in Manhattan with a burner device.

Pings from cell phone towers from both Massapequa Park and midtown Manhattan were tracked back to Heuermann.

"All of our phones, as we go along, communicate with the cell towers," says TechRadar's U.S. Editor-in-Chief Lance Ulanoff. "It kind of creates a map of where of where we are."

In January, investigators obtained Heuermann's DNA from a discarded pizza crust. They say the DNA from it matched a hair found with the body of one of the victims.

Investigators also obtained a search warrant for the suspect's email account. They say it revealed that between March 2022 and June 2023, the suspect searched more than 200 times for information on the victims' disappearances and the investigation into their murders.

The complete investigation into Heuermann consists of more than 300 subpoenas and search warrants.

Authorities say Heuermann also used a burner phone to create fake online accounts. One was allegedly used for an online dating service.

Another burner phone was used for Google search topics related to the Gilgo Beach cases, as well as topics that were sexual in nature.