RIVERHEAD, N.Y. (CBSNewYork) — Alert police officers are credited for making a ghost gun bust on Long Island.

Ghost guns are illegal weapons that can’t be traced.

Suffolk County prosecutors say all of the gun parts were bought online and assembled into lethal weapons inside a Ronkonkoma hotel room, CBS2’s Carolyn Gusoff reports.

“These are homemade weapons built from parts purchased over the internet that are not registered with law enforcement,” Suffolk County District Attorney Timothy Sini said. “Essentially made to be used in the commission of crimes.”

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Sini says this so-called ghost gun operation was uncovered thanks to two Suffolk County police officers on routine patrol.

Last month, they spotted a car illegally parked in a handicapped spot outside the hotel.

They quickly determined the car was stolen. Mail inside the car was addressed to a man staying at the hotel, so the officers knocked on his door and he let them in.

Inside, in plain view, cops say they found assembly tools and an arsenal of ghost guns, including an assault rifle and a machine gun. They also found 800 packets of heroin.

Forty-two-year-old Christopher Swanson, of Sayville, was arrested on drug and weapons charges.

His attorney, Charles Gleis, admits he has a “checkered past,” but told police the guns are his.

“I think he’s clearly a hobbyist and he had a reasonable expectation of privacy in this hotel room, and a mistake over a car rental led to more mistakes. He’s a hobbyist,” Gleis said.

“I’m sure he sells drugs for a hobby, too,” Sini said.

Sini says he is deeply troubled about the gun manufacturers who sell parts without serial numbers.

“These weapons are designed to evade detection from law enforcement, so people who have these weapons are up to no good,” he said.

Guns, he says, that can be homemade without a trace are a huge problem for law enforcement nationwide.