A soundproof room has reportedly been found in the basement of the alleged Gilgo Beach serial killer’s Long Island home.

Police reportedly discovered the room and think one of his victims may have been killed inside it, according to a New York Post article published Sunday.

In this handout provided by the Suffolk County Sheriff’s Office, Rex Heuermann poses for his booking photo on July 14, 2023. (Suffolk County Sheriff’s Office via Getty Images)

A person who used to work with the suspect, identified as Rex Heuermann, said the architect installed a concrete-lined vault at the residence. However, the space may have been where Heuermann reportedly stored nearly 300 guns.

The former colleague described it as having a massive “safe door” that also featured walls possibly two to three inches thick.

Authorities search the home of suspect Rex Heuermann on July 18, 2023, in Massapequa Park. (AP Photo/John Minchillo)

Heuermann was recently charged in the deaths of three women and is also considered the main suspect in the killing of a fourth who is connected to the “Gilgo Four” killings.

Meanwhile, law enforcement authorities have been using cadaver dogs, a backhoe, and radar to scour the man’s yard, according to the Post which shared an image of officials at work:

Breitbart News reported July 14 that hairs found on or near some of the victims were determined to belong to a woman other than any of the victims in the case because they came from Heuermann’s wife.

He was also identified as a suspect in the murders in part due to DNA left on a pizza crust he dumped in a garbage can in Manhattan. In addition, a witness in the disappearance of Amber Lynn Costello identified the vehicle the suspect was allegedly driving when she was killed.

CBS New York shared details about the Gilgo Beach murder victims in a report July 14:

According to the Post, the lengthy investigation prior to his arrest centered around the discovery of more thsn 10 sets of human remains that were dumped along Ocean Parkway.

The majority of the victims were female prostitutes, but the group included a toddler girl and an Asian man, the outlet said.

Meanwhile, ABC 7 reported Friday authorities are investigating the disappearance of an 18-year-old girl in South Carolina that happened in 2014 near a property Heuermann owned:

“It’s kinda scary because I live on this street. He kinda stays to himself. I’d see him come down the road, he’d throw his finger up and wave,” one resident told the outlet.