Rex Heuermann, the architectural consultant accused in the Gilgo Beach serial killings, was charged with a seventh murder on Tuesday morning.

Prosecutors say that he killed Valerie Mack, who had been working as an escort, more than two decades ago. Her partial remains were found in 2011.

Mr. Heuermann had already been accused of murdering five women found along the Long Island beach and another woman whose remains were found in Southampton, N.Y. He has pleaded not guilty to those crimes.

Investigators in Suffolk County have been working intently to connect him to the five other people whose remains were found near Gilgo Beach, including Ms. Mack, Karen Vergata and three unidentified victims.

Prosecutors said on Tuesday that a hair found on Ms. Mack matched the genetic profile of Mr. Heuermann’s daughter, Victoria, who would have been a little girl at the time.

Tricia Hazen, a half sister of Ms. Mack, said in an interview before the indictment that she was heartened to hear about the charges.

“He’ll get his punishment, either here or in the next world,” she said. “He has to answer to God and hopefully he’ll answer here on earth, too.”

This is a developing story and will be updated.