A New York architect previously accused of killing four women and leaving their corpses scattered along a coastal highway has been charged over the deaths of two more women.

Rex Heuermann, 60, is to appear before a judge to face charges that he killed Jessica Taylor and Sandra Costilla, two young women who were long suspected of being the victims of men preying on sex workers.

Ms Taylor disappeared in 2003 and Ms Costilla was killed in 1993.

Law enforcement officers at Rex Heuermann’s home
Law enforcement officers at Rex Heuermann’s home (Phil Marcelo/AP)

The new charges came days after police finished extensive searches of Heuermann’s Massapequa Park home and a wooded area on Long Island tied to the investigation of a string of deaths known as the Gilgo Beach serial killings.

In a court filing, prosecutors said new forensic testing methods had matched hairs found on or near both victims to a DNA profile that is a likely match to Heuermann.

Prosecutors also say they discovered a “planning document” on the hard drive found in his basement used to “methodically blueprint” his killings.

The document includes Heuermann’s concerns about leaving forensic evidence, guidance for cleaning and washing bodies, and notes on how to improve “next time”, according to the bail application

Suffolk County district attorney Ray Tierney plans to hold a news conference after the court hearing.

The charges involving Ms Costilla, who was killed 30 years ago, indicate that prosecutors believe Heuermann was killing victims for much longer longer than previously thought.

Investigators at Rex Heuermann's home in Massapequa Park
Investigators at Rex Heuermann’s home in Massapequa Park (Seth Wenig/AP)

Since late 2010, police have been investigating the deaths of at least 10 people — mostly female sex workers — whose remains were discovered along an isolated highway not far from Gilgo Beach on Long Island’s south shore.

The victims had disappeared over a span of at least 14 years, and police made only halting progress in identifying possible suspects. Investigators long said it was likely that not all of the deaths were the work of the same killer.

Some of the victims disappeared in the mid-1990s, and investigators concluded that an 11th person who disappeared in 2010 from the barrier island community of Oak Beach had accidentally drowned.

Heuermann, who lived across a bay from where the bodies were found, was arrested last July.

Prosecutors said a new investigative taskforce used mobile phone location data and DNA samples to link the architect to some of the victims. He was charged with killing four of the women: Megan Waterman, Melissa Barthelemy, Amber Lynn Costello and Maureen Brainard-Barnes.

Investigators who had searched Heuermann’s home extensively and dug up his yard last summer returned to the house again last month and spent nearly a week searching it again. They focused mostly in the basement, according to a lawyer for Heuermann’s wife.

Suffolk County district attorney Ray Tierney arrives at the courthouse in Riverhead
Suffolk County district attorney Ray Tierney arrives at the courthouse in Riverhead (Seth Wenig/AP)

That followed a search in April of a wooded area in Manorville, about 40 miles east of Heuermann’s home, linked to another Gilgo Beach victim.

Ms Taylor, 20, vanished in 2003 while working as an escort in New York City. Some of her remains were discovered in Manorville that year.

Other remains were found in a 2011 search of the beach scrub by the side of Ocean Parkway, the road where the other Gilgo Beach victims were found.

Investigators in April also spent days searching a property in the eastern Long Island hamlet of North Sea, where Ms Costilla’s body was discovered in 1993. She was 28 when she was killed and had lived in New York City.

A decade ago, Suffolk County prosecutors said publicly that they believed she had been killed by a carpenter who lived in the area, John Bittrolff, who was convicted of murdering two other women whose bodies had been found on the same part of Long Island. But he was never charged with Ms Costilla’s death due to lack of evidence, and insists he is innocent of any murders.

Heuermann, who has been in custody since his arrest, has pleaded not guilty. He had been set to return to court on June 18 for a status hearing. No trial date has been set.