The Long Island man whose tip proved key to nailing Gilgo Beach murder suspect Rex Heuermann wants to know why it took police more than a decade to follow up on his lead.

"I gave them the exact description of the truck and the dude," David Schaller said in his first interview since the accused serial killer's arrest July 13. "I mean, come on! Why didn't they use that?"

Schaller, who lived with Gilgo Beach victim Amber Lynn Costello before she disappeared in September 2010, told cops at the time that the man he believed to be her abductor looked like a hulking "ogre" with an "empty gaze" who drove a distinctive first-generation green Chevy Avalanche.

Schaller said he scuffled with the creep when the man threatened Costello, a sex worker, who locked herself in their bathroom to protect herself from her enraged "client."

On Sept. 2, 2010, she set out to meet the same customer and was never seen alive again.

"When they told me she was dead, he was the first person who jumped into my head," Schaller told The Associated Press of the then-unknown suspect. "I've been picturing his face for 13 years."

But it wasn't until last year that Suffolk County cops began properly examining the tip when they reopened their probe — under the direction of new chief and former NYPD honcho Rodney Harrison — into the cold-case murder of Costello and the 10 other people whose bodies were found between 2010 and 2011 in a marshy stretch on Long Island's South Shore.

Schaller's information helped finally identify Heuermann, a Massapequa Park architect, as a suspect in the murder of Costello and at least two of the other slain women.

Heuermann, a massive figure who drove a Chevy Avalanche, fit Schaller's description of Costello's violent "client" to a tee.

"This was crucial information, and I don't know why they didn't share it," said former Suffolk County Police Detective Rob Trotta, now a county legislator. "They made serious blunders here."

Suffolk County District Attorney Ray Tierney suggested to the AP that the tip may have gotten "lost within a sea of other tips and information."

Heuermann, a 59-year-old married dad of two who had an office in Manhattan, was charged with the deaths of Costello, Melissa Barthelemy and Megan Waterman, who police said were escorts who worked the area.

Heuermann is also the prime suspect in the death of Maureen Brainard-Barnes, police said.

Schaller said during a 2016 A&E documentary about the case that he dropped Costello off to a client who offered to pay her for the entire night.

"This one guy kept calling, and she said he wants it for the night," he said in the clip. " 'Did he throw money at you?' 'Yeah, $1,500.' It was too much money. I mean, 1,500 bucks," Schaller said.

"It just sounded like too much money," he told A&E. "It was like quarter to 10. The guy called. I walked to the edge of the property. She gave me a hug. And she bounced. She was off."

Police have now impounded two Avalanche vehicles from Heuermann's Long Island home and from a secluded piece of land he owns in rural South Carolina.

Police said Schaller's tip, along with burner phone records and DNA pulled from a half-eaten pizza crust, all helped lead them to Heuermann, who was arrested outside his Midtown offices.

Heuermann pleaded not guilty at his arraignment and is being held in jail without bail.

Additional reporting by Joe Marino