Weeks before Jeffrey Epstein killed himself in a decrepit Manhattan jail in 2019, he was found on the floor of his cell, alive but with marks on his neck.

He was placed on suicide watch, but later made a startling allegation to the guard watching over him: Epstein said his cellmate, Nicholas Tartaglione, had tried to kill him.

Tartaglione — a former police officer then awaiting trial and a possible death sentence in a quadruple murder case — had a different version of events.

He told his lawyer Epstein had tucked a suicide note inside one of the former officer's books.…