An Avalanche of evidence was hiding in plain sight.

The distinctive first-generation Chevrolet Avalanche that led cops to suspect Rex Heuermann of the Gilgo Beach murders was long visible to neighbors, passerby — and even users of online street mapping sites.

Court documents obtained by The Post Friday detailed how the key breakthrough in the 13-year-old serial killer case came when a registration search last March showed that the local married dad of two owned a first-generation model of the truck.

“This was significant, because a witness to the disappearance of [murder victim] Amber Costello identified a first-generation Chevrolet Avalanche as the vehicle believed to have been driven by her killer,” a bail application said.

That witness was Costello’s pimp — who only came forward with the key info during an interview with a special task force set up last year, Suffolk County Police Commissioner Rodney Harrison told the Daily News Saturday.

He also described the pickup-driving john as looking “like an ‘ogre’” and about 6-foot-4 tall — which “mirrors the physical attributes” of Heuermann, who is that exact height, according to the court documents ob.

In his interview last year, the pimp told cops he saw the suspect and his Avalanche while planning a September 2010 “ruse” to scare off Costello’s john by pretending to be an angry boyfriend, so they could keep the cash without sex, court documents said.

Instead, the john used a burner phone to demanded they meet the next night.

“Amber told us that he wanted to see her again, but he didn’t want to come back to the house
because of her boyfriend,” the witness told police, according to the court documents.

The burner phone was linked to Heuermann’s hometown of Massapequa Park, located about 15 minutes away from where Costerllo and the other so-called “Gilgo Four” women’s bodies were found months later in 2010.

That night would be the last time Costello, 27, was seen alive — leaving her house at the same time as a witness saw “a dark-colored truck” drive by.

Despite allegedly being seen, Heuermann made no attempt to get rid of the distinctive truck — which was still registered to him in 2022, 12 years later, the documents stated.

Archived Google Map street views from 2011 – the year after the murder investigation into the so-called “Gilgo Four” was launched – show it was regularly parked outside his 1st Avenue home, both on the street and in the driveway.

Suffolk County cops did not immediately return messages early Monday seeking clarification on exactly when info on the Avalanche was first given.

But Commissioner Harrison reportedly suggested that it only came when the unidentified pimp spoke to a task force last year, telling them they “might want to look” at the Avalanche-driving “ogre.”

“Once we got that car, who it connected to, that’s when the investigation got legs,” Harrison told the paper.

Heuermann was arrested outside his midtown Manhattan office Thursday and charged with murdering Costello, Melissa Barthelemy, 24, and Megan Waterman, 22.

He was also named the prime suspect in the death of Maureen Brainard-Barnes, 25.

Heuermann pleaded not guilty on Friday.