Gilgo Beach Alleged Serial Killer ID’d by Witness Dave Schaller in 2010

The alleged Gilgo Beach serial killer, Rex Heuermann, could have been nabbed in 2010 — 13 years before his arrest — if only cops had taken a guy named Dave Schaller seriously.

Schaller, who appears in our latest documentary — “TMZ Investigates: Gilgo Beach Serial Murders: Missed Warning Signs” — was roommates with Amber Costello, one of the “Gilgo 4.”

In 2010, Amber, a sex worker, had an encounter with a man at her home … he was paying for a lap dance. Shortly after he arrived, Amber called Dave, telling him the man was trying to rape her.

Dave quickly returned home, walked in the door, and says he saw a giant of a man — around 6’5″ — standing ominously in the living room. Dave told him to leave, and the guy refused. Dave ended up grabbing the guy, trying to get him out, and a fight ensued.

Eventually, the guy left in what Dave says was either a green or black Chevy Avalanche.

A month later, Amber had an appointment with a man and never returned home. The second she went missing, Dave knew it was the same man who was there a month earlier. Dave says Amber needed the money so she took a fatal chance.

After Amber’s body was found, Dave was interviewed by police and told them the story, describing the man in great detail, “right down to his beady-ass eyes.” He followed up 2 more time with cops, but they never chased down the lead.

Had cops run registrations for anyone in Long Island who had a green or black Avalanche, they could have then looked at the driver’s licenses of the registered owners and they would have found a 6’5″ man who fit Dave’s description to atee. That man was Rex Heuermann, and the Avalance was routinely parked in his driveway.

Authorities and others we spoke with say … it’s likely the serial killer killed other woman after his encounter with Amber Costello.