The FBI is joining an investigation into the discovery of 11 sets of human remains five years after they began to be found strewn along a remote stretch of Long Island’s Gilgo Beach, police said Thursday.

Suffolk County Deputy Police Commissioner Tim Sini made the announcement on the eve of the fifth anniversary of the discovery of the first set of remains. Police suspect one or more killers are responsible for the deaths of the 11 people, some of whom worked in the sex industry. No suspects have ever been identified in one of the most vexing murder mysteries in Long Island history.

Sini said the addition of the FBI to the so-called “Long Island serial killer” investigation is part of an overall review of all current investigations within the department.

An FBI spokeswoman confirmed the agency’s involvement in the investigation.