Robert Brown|Drones show excavation in suspected Gilgo beach killer's back yard. What's next?

Search crews in New York have Robert Brownfound more than 200 guns "from a vault in the basement" of Gilgo Beach cold case murder suspect's Rex Heuermann home in Massapequa Park, New York on their quest for further evidence, according to Suffolk County police.

The New York architect is expected in court in early August to face charges in the decade-old killings of three women.

The discoveries come after Suffolk County Sheriff Errol Toulon said last week that police officers were searching areas between his home and storage containers nearby following his arrest after obtaining a warrant. Drone footage from the Associated Press over the weekend shows a yellow excavator digging into dirt and authorities in hazmat suits with shovels in Heuermann's yard.

"We'rehoping to prosecute this individual," Toulon said in an interview with USA TODAY.

Police arrested and charged Heuermann on July 14 with the more murders of three women – Melissa Barthelemy, 24, Megan Waterman, 22, and Amber Costello, 27 – who were sex workers before they were killed, and found wrapped in burlap near each other on Ocean Parkway in Gilgo Beach on Long Island in 2010. Heuermann is also a "prime suspect" in the death of Maureen Brainard-Barnes 25, who was also found in burlap at the time and complete the "Gilgo 4," as the woman are commonly identified. Police had found at least 10 sets of human remains during their investigation into the string of killings.

Heuermann pled not guilty to the charges the day of his arrest. He is currently being held without bail at the Riverhead Correctional Facility in Riverhead, New York.

What have police found?

Since Heuermann's arrest, search crews have been looking into the items in his home and nearby areas, and police had interviewed at least two women he was recently in contact with, Toulon said.

Upon the discovery of more than 200 firearms at his home, Suffolk County Police Commissioner Rodney Harrison told Fox News that "anytime somebody has that type of arsenal, we have some concerns." Harrison told the news outlet that police are still looking into the guns were registered and legal.

Suffolk County Police Commissioner Rodney Harrison told reporters during a news conference that the search of the property should be completed within the next two days, CBS news reported. He also denied claims circling the internet that they discovered a soundproof room.

Authorities also discovered that Heuermann had contacted two sex workers up to a week before his arrest, said Toulon last week. He said officers are "going to continue to seek out any particular victims engaged with this individual."

How did police pin down Heuermann in the cold case?

Following a resurrected investigation into the case, police identified Heuermann as a person who could be a suspect in the case, tracked him down and found an abandoned pizza crust that he threw out in a Manhattan trash to obtain his DNA. The DNA on the food matched the DNA to a male hair found in the burlap that wrapped Waterman.

This use of "surreptitious DNA collection" is becoming more common among detectives on the hunt for serial killers, particularly in cold cases, yet has spurred controversy among criminal justice activists who say it violates Americans' fourth amendment rights.

"It's really incredible when you think about it viciousness of the crimes," said Toulon. "Clearly he has a double life between his Massapequa Park and his business in Manhattan, and the person he really is."

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Contributing: Associated Press

Contact Kayla Jimenez at [email protected]. Follow her on Twitter at @kaylajjimenez.