US Attorney General Bill Barr has said there were "serious irregularities" at the jail where Jeffrey Epstein died of an apparent suicide, and pledged to pursue any co-conspirators in the sex trafficking case.
"I was appalled and indeed the whole department was, and frankly angry, to learn of the Metropolitan Correctional Center's failure to adequately secure this prison," Mr Barr told reporters.
"We are now learning of serious irregularities at this facility that are deeply concerning and demand a thorough investigation.
"The FBI and office of the inspector general are doing just that. We will get to the bottom of what happened and there will be accountability," he added.
Mr Barr's comments came after media reports said Epstein had been taken off suicide watch following an apparent suicide attempt last month.
US newspapers also reported that prison guards were working overtime due to major staff shortages at the facility and that Epstein had been left without a cellmate, which was against protocol.
Epstein, a convicted pedophile who hobnobbed with countless politicians and celebrities over the years, was found dead in his cell Saturday while awaiting trial on federal charges he trafficked underage girls for sex.
The discovery came a day after a court released documents in which one of Epstein's alleged victims claimed she was forced to have sex with well-known American political and business personalities. They have all denied the allegations.
Even though Epstein's criminal prosecution is over, Mr Barr said prosecutors would pursue cases against anyone else involved in his alleged crimes.
"Let me assure you this case will continue on against anyone who was complicit with Epstein. Any co-conspirators should not rest easy. The victims deserve justice and they will get it," he said.
Epstein, 66, had been charged with one count of sex trafficking of minors and one count of conspiracy to commit sex trafficking of minors.
Prosecutors said Epstein sexually exploited dozens of underage teens, some as young as 14, at his homes in Manhattan and Palm Beach, Florida, between 2002 and 2005.
The young women were paid hundreds of dollars in cash to massage him, perform sexual acts and to recruit other girls, prosecutors alleged.
The wealthy financier, who faced up to 45 years in prison if convicted, denied the charges.
Epstein - whose friends included Donald Trump, former president Bill Clinton and Britain's Prince Andrew - had been convicted in 2008 in a Florida state court of paying young girls for sexual massages at his Palm Beach mansion.
Those men have all denied knowing anything about Epstein's alleged crimes.