Mr. Epstein’s death is the subject of four federal investigations, including by the Justice Department’s inspector general and the F.B.I. The attorney general, William P. Barr, said there were “serious irregularities” in how prison officials handled his supervision.

On July 23, Mr. Epstein was found on the floor of his cell with bruises on his neck and was placed in the prison’s suicide prevention program, where he was under a 24-hour watch in a special cell in which there were no bedclothes or other material that could be fashioned into a noose.

But six days later, prison officials determined he was no longer a threat to himself and returned him to a cell in a special housing unit known as 9 South. He was supposed to have been housed with a cellmate and to have been monitored every half-hour by the two guards who patrolled the wing.

The night before he was found, however, he had been left alone after his cellmate was transferred. The two employees assigned to guard him had not checked on him for about three hours before he was discovered.

Officials said the employees, who have been placed on leave, were sleeping for some or all of that time.

Mr. Epstein had pleaded not guilty and been denied bail. Prosecutors in Manhattan said he lured dozens of underage girls into giving him erotic massages and engaging in other sexual acts in the early 2000s at his mansions in New York City and Palm Beach, Fla.

The girls were paid hundreds of dollars in cash for the encounters and, once recruited, were asked to return to his homes several times, where they were abused again, the indictment against him said.