The former friend of Presidents Bill Clinton and Donald Trump was being held in the Metropolitan Correctional Center pending his trial on charges of sex trafficking of minors and conspiracy to sex traffic minors.

Epstein, 66, was found Saturday morning in his jail cell in cardiac arrest and was transferred to a New York hospital, where he was pronounced dead, according to NBC News. Sources told NBC that Epstein hanged himself.

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

Barr, who said in a statement over the weekend that he was "appalled" by Epstein's death, also fired a warning shot to anyone who may have been involved in the wealthy financier's alleged crimes.

"We will get to the bottom of what happened," Barr vowed in blistering opening remarks at a police event in New Orleans, "and there will be accountability."

Attorney General William Barr said Monday that there were "serious irregularities" at the Manhattan federal jail where Jeffrey Epstein, an accused child sex trafficker, apparently killed himself over the weekend .

Those charges were lodged by Manhattan federal prosecutors and made public last month after his arrest at a New Jersey airport, where Epstein had flown into from Paris on his private plane.

Just a few weeks before his death, Epstein had been discovered lying semiconscious in the fetal position in his cell. He reportedly had marks on his neck, raising the possibility that he had attempted to kill himself then.

Epstein was subsequently transferred to suicide watch — but outlets reported that he was taken off suicide watch just six days later. He had reportedly been alone in his cell and was not monitored by guards who were supposed to check on him every 30 minutes.

The New York Times also reported that Epstein's cellmate had been transferred shortly before the apparent suicide, leaving him alone.

Barr, keynote speaker at the National Fraternal Order of Police's biennial conference in New Orleans, said Epstein's case "was very important to the Department of Justice and to me personally," as well as to the FBI and the federal prosecutors preparing to take the case to trial.

"Most importantly, this case was important to the victims who had the courage to come forward and deserved the opportunity to confront the accused in the courtroom," Barr said.

"I was appalled, and indeed the whole department was, and frankly angry, to learn of the MCC's failure to adequately secure this prisoner," Barr said.

He continued: "We are now learning of serious irregularities at this facility that are deeply concerning and demand a thorough investigation. The FBI and the Office of Inspector General are doing just that."

Barr also assured that Epstein's case, and the cases related to his alleged sex crimes, will continue on "against anyone who was complicit with Epstein."

The wealthy financier was accused in the New York case of sexually abusing dozens of underage girls at his mansions on the Upper East Side of Manhattan and in Palm Beach, Florida, between 2002 and 2005. He had pleaded not guilty to the two counts against him, which carried a maximum possible sentence of 45 years if convicted.

A decade earlier, Epstein had pleaded guilty to Florida state charges of prostitution with an underage girl, which allowed him to avoid more severe federal charges.

He was sentenced to 13 months in a state prison, and was allowed out on work release for most days during his incarceration. Alex Acosta, who was the top prosecutor in Florida at that time, resigned as Trump's Labor secretary last month amid an outcry over Epstein's lenient plea deal.

On Friday, a federal appeals court publicly disclosed nearly 2,000 pages of documents related to Epstein that had previously been entered under seal in a case involving one of Epstein's accusers, Virginia Giuffre, and Ghislaine Maxwell, the late money manager's alleged procurer of underage girls.

The documents included flight records showing that Trump had flown on Epstein's private plane in 1996; previously released flight logs showed Clinton had been on the plane multiple times.

The death of Epstein — possibly the most high-profile and highly scrutinized prisoner in the country — lit social media ablaze, fueling rampant speculation and conspiracy theories.

Trump himself retweeted a baseless conspiracy that tried to connect Clinton to Epstein's death, despite Barr saying in a statement that it was a suicide. Lynne Patton, a senior Housing and Urban Development official, suggested on Instagram that Hillary Clinton was responsible — also without any evidence.

The New York City medical examiner performed an autopsy of Epstein, but said its determination is "pending further information at this time."