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. He handed the note over to his legal team but its existence got scant mention in the years afterwards — even after Epstein's suicide in a different cell about three weeks later was scrutinized by federal investigators and a skeptical public.…