Six weeks after a renewed investigation into the Gilgo Beach murders, the meticulous work of dogged investigators tied an old clue to a new name.

LIVE BLOG: Updates on the case as they happen

It all started with a revived tip from one of the last people to see victim Amber Costello alive in September 2010. The witness told police that one of Costello’s clients parked a green Chevrolet Avalanche in her driveway shortly before her disappearance. The vehicle was believed to be driven by her killer.

Investigators now know that Rex Heuermann drives that type of car, but for 13 years, all they had was a description of the vehicle and the suspect. The witness told police the suspect resembled an “ogre” at six feet six inches tall with “dark bushy hair” wearing “big oval style 1970’s type eyeglasses.”

WATCH: DOCUMENTARY AND BACKGROUND INFORMATION - Gilgo Beach: Unsolved

Police had no license plate number and no name.

Investigators spent years recovering and analyzing data from cell towers. They connected cell site locations with phones used to contact some of the victims.

Police combed through thousands of cell tower records and phone calls, until they finally narrowed it down to hundreds of matching calls. They noticed a cluster of these calls coming from an area in Massapequa Park.

Investigators felt they finally had a small break in the case.

“Just being able to get into that box, the size of it is anywhere between two square miles. It was hard to kind of figure that out right off the wind,” said Suffolk Police Commissioner Rodney Harrison.

Now that the Gilgo Beach Homicide Investigation Task Force had an area to focus on, a state police investigator searched for anyone living in this box who owned a green Chevy Avalanche. The investigator searched through car registration records to find Heuermann, who also matched the suspect description.

Using 300 subpoenas and search warrants, police dug into Heuermann’s background. They learned his cellphone was often in the same areas, around the same time, as burner phones that were used to contact some of the victims, according to court documents. His cellphone location also matched up with some of the victims’ cellphone locations after they disappeared, police say.

Archived Google map photos show Heuermann’s green Chevy Avalanche parked in plain sight outside of his Massapequa Park home in November 2011—15 months after Costello disappeared.

“They did a phenomenal job taking a look at that vehicle and doing what's called a TLO check and being able to attach that vehicle to the Massapequa Park box that we've identified based upon the burner phones that were connected within that area,” Commissioner Harrison said. “Sciences, technology, the team effort, the leadership of Detective Lieutenant Kevin Beyrer, helped us get to this point in the investigation.”