“We will get to the bottom of what happened,” he added. “There will be accountability.”

Mr. Barr did not offer additional information about the problems at the jail, but questions have been raised about why Mr. Epstein had been taken off suicide watch just days after apparently trying to kill himself and then was left alone in a cell without close supervision.

Mr. Barr also said Mr. Epstein’s suicide would not halt the investigation into other people who might have helped him traffic teenage girls for sex. On Monday, F.B.I. agents and New York detectives raided Mr. Epstein’s private, 70-acre island in the United States Virgin Islands , looking for documents, photographs, videos, computers and other materials, people briefed on the matter said.

“Any co-conspirators should not rest easy,” Mr. Barr said. “The victims deserve justice and they will get it.”

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 two law-enforcement officials 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.