An architect charged with a string of slayings known as the Gilgo Beach killings has been accused of taking the life of a fourth woman, a Connecticut mother-of-two who vanished in 2007 and whose remains were found more than three years later along a coastal motorway in New York.

Rex Heuermann has been formally charged over the death of Maureen Brainard-Barnes, months after being labelled the prime suspect in her death when he was arrested in July over the deaths of three other women.

In court on Tuesday, Heuermann wore a dark suit and did not say anything during proceedings.

He will continue to be held without bail.

Suffolk County district attorney Ray Tierney, left, inside Judge Timothy Mazzei’s courtroom at Suffolk County Court in Riverhead on Tuesday, when alleged Gilgo Beach Killer Rex Heuermann was indicted in the death of Maureen Brainard-Barnes
Suffolk County district attorney Ray Tierney, left, inside Judge Timothy Mazzei’s courtroom at Suffolk County Court in Riverhead on Tuesday, when alleged Gilgo Beach Killer Rex Heuermann was indicted in the death of Maureen Brainard-Barnes (Newsday via AP)

The judge set the next court date for February 6.

Heuermann has maintained his innocence from “day one” and looks forward to defending himself in court, lawyer Mike Brown said.

He entered a not guilty plea on the latest charges.

Mr Brown said he is still reviewing new information presented by prosecutors in court documents on Tuesday morning.

Prosecutors said Heuermann also searched the internet for phrases that suggested he was afraid of getting caught, including “how does cell site analysis work”, “Gilgo news”, “how cell phone tracking is increasingly being used to solve crimes” and phrases with the term “Long Island serial killer”.

Ms Brainard-Barnes, 25, who was once employed as a dealer at the Foxwoods Resort Casino, left her hometown of Norwich, Connecticut, on July 9 2007 and went to Manhattan for sex work, with plans to return the next day, according to friends, who became concerned when she uncharacteristically stopped using her phone.

She never returned.

Heuermann was arrested on July 14 and charged with killing Melissa Barthelemy, Megan Waterman and Amber Lynn Costello, three women who authorities say were also sex workers.

Heuermann’s lawyer said he has denied committing the crimes.

He previously pleaded not guilty to killing Ms Barthelemy, Ms Waterman and Ms Costello.

Ms Brainard-Barnes was the first of the four women to disappear.

Their remains were found along the same quarter-mile stretch of parkway in the Gilgo Beach area of Jones Beach Island in 2010.

Additional searching turned up the remains of six more adults and a toddler who was the child of one of the victims.

Police concluded that an 11th person found dead in a tidal marsh on the same barrier island accidentally drowned.

Investigators have said Heuermann, who lived in Massapequa Park across the bay from where the bodies were found, was probably not responsible for all the deaths.

Rex Heuerman, right, listens in court on Tuesday
Rex Heuerman, right, listens in court on Tuesday (James Carbone/Newsday via AP)

Some of the victims disappeared in the mid-1990s.

Investigators zeroed in on Heuermann when a new task force ran an old tip about a Chevy Avalanche pick-up truck through a vehicle records database.

A hit came back identifying such a vehicle belonging to Heuermann, who lived in a neighbourhood police had been focusing on because of mobile phone location data and call records, authorities said.

With the tip breathing new life into the investigation, authorities charted the calls and travels of multiple mobile phones, picked apart email aliases, delved into search histories and collected discarded bottles — and even a pizza crust — for advanced DNA testing, according to court papers.

Detectives said Heuermann’s DNA on the pizza crust matched a hair found on a restraint used in the killings.

Police said other evidence linked Heuermann to the victims, including burner phones used to arrange meetings with the slain women.

After the arrest, investigators spent nearly two weeks combing through Heuermann’s home, including digging up the yard, dismantling a porch and a greenhouse and removing many contents of the house for testing.

Investigators found hundreds of electronic devices during their lengthy search of Heuermann’s home, according to court documents released on Tuesday.

Prosecutors say the devices contained a collection of bondage and torture pornography.