The Metropolitan Correctional Center houses about 800 people awaiting either trial or sentencing in New York City, and over the years its inmates have included high-profile terrorists, white-collar criminals and organized crime figures.

Mr. Epstein had been held there since his arrest on July 6 on federal charges that he sexually abused and trafficked girls in the early 2000s. Judge Richard M. Berman of Federal District Court had denied him bail, rejecting his request to be detained at his Upper East Side mansion as he awaited trial.

One federal prison official with knowledge of the incident confirmed Mr. Epstein had been taken off suicide watch recently and was being held alone in a cell in a special housing unit. The official, who spoke on the condition of anonymity for fear of being fired, said guards found Mr. Epstein in an otherwise empty cell during morning rounds. He had hanged himself and he appeared to be dead.

It would have been extremely difficult for Mr. Epstein to harm himself had he still been on suicide watch, a second prison official said, also speaking on the condition of anonymity for fear of dismissal.

Inmates on suicide watch are generally placed in a special observation cell, surrounded with windows, with a bolted down bed and no bedclothes, the official said. A correction officer — or sometimes a fellow inmate trained to be a “suicide companion” — is typically assigned to sit in an adjacent office and monitor the inmate constantly.

Robert Gangi, an expert on prisons and the former executive director of the Correctional Association of New York, said guards also generally take shoelaces and belts away from people on suicide watch. “It's virtually impossible to kill yourself,” Mr. Gangi said.

Inmates can only be removed from the watch when the program coordinator, who is generally the chief psychologist at the facility, deems they are no longer at imminent risk for suicide, according a 2007 Bureau of Prison document outlining suicide prevention policies. The inmates cannot be removed from the watch without a face-to-face psychological evaluation.