Rex Heuermann, who was arrested last summer and has been accused of murdering four women in the Gilgo Beach serial killings on Long Island, was indicted Thursday on murder charges in the deaths of two more women.

Mr. Heuermann, 60, who has pleaded not guilty to all charges in connection with the first four women’s deaths, has remained in jail for nearly a year awaiting trial. In the meantime, investigators turned to the six other victims — four women, a man and a toddler — whose remains, like those of the first four women, were found along Ocean Parkway by Gilgo Beach.

On Thursday, Mr. Heuermann was charged with killing one of them: Jessica Taylor, whose partial remains were found near Gilgo Beach in 2011 and then linked to other partial remains found eight years earlier in a remote wooded area in Manorville, a 45-minute drive east.

He was also charged with killing Sandra Costilla, a 28-year-old New York woman whose remains were found in 1993 in the Hamptons. Her long unsolved murder had not previously been associated with the Gilgo Beach investigation.

The new indictment followed a recent flurry of activity in the investigation: a nine-day canine search completed last month in Manorville and a wooded area in Southampton where Ms. Costilla’s body was found. Last month, investigators also conducted a six-day search of Mr. Heuermann’s home in Massapequa Park, which had been exhaustively searched for two weeks last summer after his arrest.

The Gilgo investigation dates back to late 2010, when investigators discovered the first of 10 victims left along a desolate stretch of Ocean Parkway running east from Jones Beach.