Walk-In Vault Found in Rex Heuermann’s Basement During Search of Property: Police

Nearly two weeks into their search Rex Heuermann’s home on Long Island, police said they’ve found a vault inside the suspected Long Island Serial Killer’s home and have begun digging up his backyard.

Suffolk Police Commissioner Rodney Harrison told reporters Monday that Heuermann, a 59-year-old architect and father of two, kept guns inside the walk-in basement vault, which had a “big iron door,” ABC News reports.

Police have found more than 200 guns in Heuermann’s home, according to the outlet. Heuermann only had permits for 92 of the weapons.

“There have been items that we have taken into our possession. That makes it fruitful,” Harrison said of the search, according to local WABC. The outlet reports investigators have also dismantled a wood deck in Heuermann’s backyard, as they continue searching for clues in the Gilgo Beach murder case.

CBS News also reports that drone footage showed investigators digging a large hole in the suspect’s backyard, as they’ve reportedly been investigating whether Heuermann killed any of his alleged victims at his suburban Massapequa Park home.

Heuermann was arrested earlier this month and charged with three counts of first-degree murder and three counts of second-degree murder in the deaths of Amber Costello, 27, Melissa Barthelemy, 24, and Megan Waterman, 22. He has pleaded not guilty. Police say DNA evidence connects him to the murders.

There were earlier reports about a soundproof room being found on Heuermann’s property, too, but authorities disputed that claim this week.

“I believe that the soundproof room and the vault, that message got misconstrued, but there is a vault. There is no soundproof room,” Suffolk County Police Commissioner Rodney Harrison said, Fox News reports.

Heuermann also remains the primary suspect in the murder of 25-year-old Maureen Brainard-Barnes. All four women were sex workers who went missing and whose remains were later discovered on Gilgo Beach more than a decade ago.

At least 10 bodies were discovered at the beach, but investigators have said not all of them are believed to be connected to the same killer.

The case remained unsolved for more than a decade and gained notoriety after the investigation became the focus of author Robert Kolker’s 2013 bestselling nonfiction book Lost Girls, and later a true crime Netflix movie of the same name.

The killer allegedly used four separate burner phones to contact the women and “lure them out to Massapequa,” Suffolk County District Attorney Ray Tierney previously told PEOPLE. “Then he would murder them, and then he would discontinue the use of the burner phone. He did that four times.”

Tierney said investigators also found Heuermann had a “concerning” internet search history, which allegedly showed the Massapequa man “obsessively” looked up his victims and their siblings. A number of the victims’ family members have said they received taunting phone calls from a man who claimed to be the killer.

Heuermann had little to say when he was taken into custody by police earlier this month, however.

Harrison told PEOPLE Heuermann was “very quiet” and mostly “kept to himself” when he was arrested.

“I believe once one of our officers said he had him under arrest, he said, ‘Why?’ But that’s pretty much the most I’m being told what he said,” the police commissioner said, adding, “He’s still been quiet since he’s been over at Riverhead [Correctional Facility].”

*With reporting by Christine Pelisek.