John Bittrolff (born July 1, 1966) is an American convicted murderer and former suspect in the Gilgo Beach serial killings case.

He was also a suspect in the murder of a third woman, Sandra Costilla, prior to the capture of alleged serial killer Rex Heuermann.

Believed by authorities to be a sex worker, she was beaten, strangled to death and left naked in the woods, near the William Floyd Parkway.

[13] On June 6, 2024, Gilgo Beach serial killings suspect Rex Heuermann was charged with Costilla's murder.

On July 13, 2023, another man, Rex Heuermann, a long-time resident of Massapequa Park on Long Island, was arrested and subsequently charged with six murders attributed to the Long Island serial killer, including for the murders of Melissa Barthelemy and Sandra Costilla.