No correctional officer had checked on Mr. Epstein for several hours before he was found, even though guards were supposed to look in on prisoners in the protective unit where he was housed every half-hour, a prison official and a law-enforcement official with knowledge of the detention said, speaking on the condition of anonymity.

In addition, only one of the two people guarding the Special Housing Unit — known as 9 South — normally worked as a correctional officer, according to three prison officials with knowledge of the case. The officials did not say what sort of job the other employee usually worked.

A New York Times investigation published last year detailed this practice, under which federal prisons are so strapped for correctional officers that they regularly compel teachers, nurses, secretaries and other support staff members to step in. The practice has grown at some prisons as the Trump administration has curtailed the hiring of correctional officers.