The US Department of Justice has launched an investigation into the death of Jeffrey Epstein, the disgraced billionaire accused of operating an international sex trafficking ring while abusing countless young girls.

Epstein, 66, was found on Saturday morning unresponsive inside a cell at the Metropolitan Correctional Centre in Manhattan, according to the US Bureau of Prisons. He was pronounced dead at the New York Downtown Hospital shortly after, ABC News reported.

Attorney general William Barr said he was “appalled” by Epstein’s death in a statement announcing the Justice Department’s inspector general would be investigating the circumstances of the apparent suicide.

“I was appalled to learn that Jeffrey Epstein was found dead early this morning from an apparent suicide while in federal custody,” the attorney general said. “Mr Epstein’s death raises serious questions that must be answered.”

“In addition to the FBI’s investigation, I have consulted with the inspector general who is opening an investigation into the circumstances of Mr Epstein’s death,” the statement continued.

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There was no official confirmation by Sunday afternoon that Epstein had in fact died by suicide, although numerous reports said officials believed he hanged himself. Just three weeks earlier, the billionaire – who was scheduled to stand trial next year over sex trafficking and conspiracy charges – was found unresponsive in his cell with seemingly self-inflicted bruises on his neck.

The lack of official confirmation led to a brewing of right-wing conspiracy theories alleging the reported death had something to do with Bill Clinton, the former US president, who once was a prominent member of the billionaire’s inner circle, along with other world leaders and powerful elite.

The conspiracy theories were given a speakerphone by the White House, as Donald Trump retweeted posts that appeared to refute the death being a suicide while linking Mr Clinton to Epstein.

“Died of SUICIDE on 24/7 SUICIDE WATCH? Yeah right!” One tweet read that the president shared, despite reports indicating Epstein was not on suicide watch at the time of his death.

Epstein “had information on Bill Clinton [and] no he’s dead,” the tweet continued.

Hashtags like #EpsteinSuicideCoverUp and #TrumpsBodyCount were also trending on Twitter across the country on Sunday afternoon.

Mr Trump himself has been photographed and seen on video with Epstein, in one instance ogling women at a party with the billionaire in front of media cameras.

Epstein was facing 45 years in prison over accusations he sexually abused dozens of underage girls, with many of those victims now expressing frustration over the billionaire’s reported death.

“I am extremely mad and hurt thinking he once again thought he was above us and took the easy way out ... I still can’t wrap my head around the fact that’s really true,” Jena-Lisa Jones, who was allegedly raped by Epstein at the age of 14, said in a statement to ABC News. “God will have his judgement now.”

“I am angry Jeffrey Epstein won’t have to face his survivors of his abuse in court,” Jennifer Araoz, who said she was raped by Epstein at the age of 15, also told the news outlet. “We have to live with the scars of his actions for the rest of our lives, while he will never face the consequences of the crimes he committed the pain and trauma he caused so many people.”

Epstein’s suicide watch reported ended after July following daily psychological assessments, CNN reported. He had since been living in the Special Housing Unit of the jail.

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According to Rod Rosenstein, the former deputy attorney general, “paedophiles facing federal criminal charges are at high risk for suicide”.

The former official wrote on Twitter on Saturday: “It happened in several of my Maryland cases when defendants were released on bail.