Attorney General William Barr said Monday that he was "angry" to find out about accused child sex trafficker Jeffrey Epstein's death while in federal custody at the Metropolitan Correctional Center over the weekend and vowed once again to find out how it happened.

While giving an address at the Fraternal Order of Police's annual conference in New Orleans, America's top cop paused to address the ongoing question of how Epstein's death occurred while in federal custody.

"This sex trafficking case was very important to the Department of Justice and to me personally," Barr said. "It was important to the dedicated prosecutors in the Southern District of New York and to our FBI agents who investigated the case and were preparing it for trial."

"Most importantly, this case was important to the victims who had the courage to come forward and deserve the opportunity to confront the accused in the courtroom," the attorney general continued. "I was appalled — and indeed, the whole department was — and frankly angry, to learn of the MCC's failure to adequately secure this prisoner.

"We are now learning of serious irregularities at this facility that are deeply concerning and demand a thorough investigation," Barr said. "The FBI and the office of inspector general are doing just that. We will get to the bottom of what happened, and there will be accountability."

A transcript of Barr's full remarks at the event was released shortly after by the Justice Department. Video is available below:

After news of Epstein's death broke over the weekend, Barr said Saturday in a formal statement: "Epstein's death raises serious questions that must be answered" and that there would be both an FBI and inspector general's investigation into the matter.

The circumstances surrounding the child sex trafficking suspect's weekend death, however, remain a mystery. There is no footage of what happened to the prisoner, law enforcement officials told the New York Post. Furthermore, a new report notes that Epstein's cellmate was transferred to another part of the prison before Epstein's death. Also, Epstein's death also comes on the heels of court documents in which two high-profile Democratic politicians had been named by one of the billionaire's accusers, adding to suspicions about the timing of the alleged suicide.

"Given Epstein's previous attempted suicide, he should have been locked in a padded room under unbroken, 24/7, constant surveillance," Sen. Ben Sasse, R-Neb., said in a letter to Barr on Saturday. "Obviously, heads must roll."