When the authorities announced the arrest of Rex Heuermann last summer in four of the Gilgo Beach serial killings, the relieved families of the slain women stood with them.

But along that desolate stretch of Long Island beach, at least 10 bodies were found. And loved ones of the other victims await answers more than a dozen years later.

“The Gilgo case is still mostly unsolved,” said Lorraine Paulino, 54, who said she met one of the six victims, Karen Vergata, shortly before she disappeared.

To crack the cold case, the task force that formed in early 2022 focused on the so-called Gilgo Four, the most immediately solvable cases, which led to the arrest last summer of Mr. Heuermann, 60.

“When you start a puzzle, you have to start with the most obvious pieces,” the Suffolk County district attorney, Ray Tierney, said in an interview.

The uniform way the bodies were treated bore the hallmarks of a serial killer. Investigators had a strong set of clues including DNA and mobile phone data linking the four bodies to Mr. Heuermann, who has pleaded not guilty to killing the women.