Police officers were seen swarming the basement of a 59-year-old architect who prosecutors alleged is responsible for the murders of at least three women whose remains were discovered hidden in the marsh near New York's Gilgo Beach more than a decade ago.

Rex Heuermann, known by neighbors as a quiet man with a family that kept to themselves, had a dark secret, according to police. 

He is accused of killing three young women and dumping their remains in a remote waterfront area about 45 miles east of Manhattan. Officers spent the weekend searching through his unkempt home – which stands out in a neighborhood of finely maintained suburban homes, around the corner from an elementary school and the former police academy.

GILGO BEACH SERIAL KILLER SUSPECT HAD ARSENAL OF WEAPONS, TOP COP SAYS

WATCH: Police in New York search suspected Gilgo Beach killer Rex Heuermann's home in Massapequa Park

Photos and videos taken at his home in Massapequa Park show police carried numerous boxes of evidence out, including cabinets and at least one toolbox they dragged up his basement stairs.

"He had an arsenal in a vault that he had downstairs," Suffolk County Police Commissioner Rodney Harrison told Fox News Monday. Investigators had not yet determined whether all the weapons were obtained legally, he added.

Gilgo Beach murders suspect Rex Heuermann mugshot

Rex Heuermann's mug shot. (Suffolk County Sheriff’s Office via AP)

The architect, who in a creepy interview long before his arrest once said his favorite tool was a hammer because it was good for "persuasion," also had numerous tool boxes that the police serving a search warrant took interest in.

ACCUSED GILGO BEACH KILLER NICKNAMED PETER FROM ‘FAMILY GUY’ BY CO-WORKERS: SOURCE

Harrison said police seized more than 200 firearms from his home as part of the investigation. Heuermann is said to have been an avid duck hunter – and District Attorney Ray Tierney revealed Friday that the burlap material the victims were dumped in was the kind used in duck blinds.

Fox News drone video shows investigators carrying evidence out both the front door and the back basement stairway.

They were also spotted searching a storage unit nearby in Amityville, New York, on Monday.

A man who answered a call to the phone number for the storage unit repeatedly answered questions with, "We have no statement" regarding the search Monday.

Gilgo Beach murders victims Amber Costello, Maureen Brainard-Barnes, Melissa Barthelemy, Megan Waterman

Gilgo Beach murder victims Amber Costello, top left, Maureen Brainard-Barnes, top right, Melissa Barthelemy, bottom left, and Megan Waterman. (Suffolk County Police Department)

More than a dozen neighbors told Fox News Digital over the weekend that they had seen Heuermann on a near daily basis as he commuted to and from Manhattan on the Long Island Rail Road – which has a station just blocks from his deteriorating home.

READ: CASE AGAINST REX HEUERMANN

Heuermann grew up in the house and bought it from his mother in the 1990s.

He faces six murder charges in the deaths of Melissa Barthelemy, Megan Waterman and Amber Costello – a first- and second-degree charge for each victim.

Drone footage of officers searching Gilgo suspect house

Police officers from NYSP, Nassau and Suffolk County police searched suspected killer Rex Heuermann's home Friday, removing evidence in bags. Heuermann has been charged with murder in connection to the deaths of the "Gilgo Four." (Fox News )

The hulking hunter remains the top suspect in at least one other Gilgo Beach homicide, the slaying of Maureen Brainard-Barnes, according to prosecutors.

The murders remained unsolved more than a decade after the search for missing escort Shannan Gilbert, 24, first led police to the bodies of sex workers and other victims east of New York City. 

Police cars parked outside storage unit in Amityville, NY

Police also searched a storage unit in Amityville, New York, on Monday, July 17, 2023. Officers roped off the parking lot, but investigators could be seen working out of a tent near one of the units. (Michael Ruiz/Fox News Digital)

Following a series of harrowing 911 calls from Gilbert, search teams found the first four victims, dubbed the "Gilgo Four." They were Costello, 27, Brainard-Barnes, 25, Waterman, 22 and Barthelemy, 24.

In March 2011, the partial remains of 20-year-old Jessica Taylor were found near Gilgo Beach. Authorities said part of Taylor’s body was discovered eight years earlier and 40 miles away in Manorville, New York.

Heuermann handout reuters

Rex Heuermann, an architect who lived a 20-minute drive from Gilgo Beach in Massapequa Park, appears in what investigators decribe as "selfie" photographs taken from the fictitious Springfieldman9 AOL account, as part of a bail application by the Suffolk County District Attorney's office July 14, 2023. ( Suffolk County Court/Handout via REUTERS)

Days later, three more sets of human remains were discovered alongside Ocean Parkway, which runs along Long Island's south shore beaches.

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The first was 24-year-old Valerie Mack, whose partial remains had also been found in Manorville years earlier. An unidentified toddler was found near Mack, according to the official website dedicated to the case.

Two miles west, police discovered the skeletal remains of an unidentified Asian man — or transgender woman — believed to be 17 to 23 years old.

A week later, in April 2011, two more sets of partial remains were found along Ocean Parkway. The first were those of the woman known as "Peaches," believed to be the mother of the toddler found the week before. Part of her body had been previously discovered in Hempstead Lake State Park in 1997. The second was the skull of a woman who was linked to remains found on Fire Island in 1996.