Who is Gilgo Beach serial killer suspect Rex Heuermann?

The Long Island man busted for the notorious Gilgo Beach murders is an architect who calls himself a “troubleshooter” working alongside New York City’s Department of Buildings.

Rex Heuermann, 59, was busted at his home in Massapequa Park, numerous sources told The Post Friday.

He had been on the special Gilgo Beach Homicide Investigation Task Force for at least a year — and was arrested after being linked by DNA, one source said.

Heuermann is the president of his own Fifth Ave.-based company, RH Architecture Design, which he’s had since 1994 — 10 years before the Long Island murders.

“I’m a troubleshooter born and raised on Long Island,” the portly, dark-haired architect told a French YouTuber last year.

He is also an avid furniture maker inspired by his dad, whom he described as a cabinet-maker who’d also been an “aerospace engineer who built satellites.”

One neighbor, Barry Auslander, 72, told The Post Friday that Heuermann looked like an “average guy who had a family and went to work.”

“He grew up here. I never thought he was anything but a businessman,” he said.

Heuermann stressed that he did not work directly for the city, but as a “facilitator” — especially out-of-town companies who are “a little afraid of the city,” he said, chuckling throughout the interview.

“They’re overwhelmed by the city,” he said — while also mocking city workers for not being able to “understand their own codes, their own laws.”

“Part of my job became, educate the city,” he reckoned. “That’s something we’ve done ever since,” he said, saying his main skill was “patience.”

According to his website, Heuermann has also “provided services to other city agencies, not-for-profit agencies, builders, developers and individual owners of buildings.”

“His clients include Catholic Charities, NYC-DEP Sewerage Treatment and American Airlines and other major tenants at the JFK International Airport.,” it states.

RH Architecture Design did not reply to messages early Friday.