Jeffrey Epstein - REUTERS

Jeffrey Epstein, the disgraced American financier charged with child sex trafficking, took his secrets to the grave after apparently hanging himself in a prison cell while awaiting trial.

The FBI launched an investigation into the death as a row erupted over how Epstein was allowed to cheat justice, as victims expressed anger at being denied their day in court.

Epstein's death meant the full story of the powerful political figures and celebrities potentially connected to his alleged sex ring may never be told.

His lawyers initially refused to rule out foul play, fueling conspiracy theories that his death will silence further damaging revelations.

Epstein, 66, died the day after a tranche of documents were released in a civil case in which Virginia Giuffre, who claimed to have been his teen "sex slave," had sued Ghislaine Maxwell, 57, Epstein's former girlfriend, for defamation.

Mrs Giuffre, now 35, had claimed to have had sex with the Duke of York when she was 17. The duke has always categorically denied the allegations, which were struck from court record in 2015 after being described as "immaterial and impertinent" by the judge.

Epstein was found unresponsive in his cell at the Metropolitan Correctional Center in Manhattan at 6.30am on Saturday. It was "an apparent suicide", the US department of justice said.

The Metropolitan Correctional Center in Manhattan Credit: AFP

Prison officials tried unsuccessfully to resuscitate him, and he was seen being wheeled into New York Presbyterian-Lower Manhattan Hospital on a stretcher an hour later. He was pronounced dead on arrival.

Bill Barr, the US attorney general, was said to be "livid and appalled" and demanded to know how Epstein was allowed to die. He said the death "raises serious questions that must be answered."

In a statement the justice department said: "The FBI is investigating the incident." The department of justice's inspector general also opened an investigation.

Mrs Giuffre's lawyer called for investigations into associates of Epstein to continue.

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Sigrid McCawley said: "We are hopeful that the government will continue to investigate, and will focus on those who participated and facilitated Epstein’s horrifying sex trafficking scheme that damaged so many."

Officials with the US Attorney’s office in Manhattan indicated the Epstein investigation would continue despite his death.

Last month the US government said it was pursuing an "ongoing investigation of uncharged individuals" in connection with the Epstein case.

Epstein had previously been found with bruises on his neck on July 25 following an apparent suicide attempt.

He had been in a shared cell with an inmate called Nicholas Tartaglione, a former police officer charged with murder, but it was unclear whether they were still in the same cell.

Epstein was in a special high security unit, which has housed high profile prisoners including the Mexican drug lord Joaquin "El Chapo" Guzman.

Prison officers on the unit were supposed to check all prisoners every 30 minutes, but the procedure was reportedly not followed on the night Epstein died.

Suicide watch would involve checking a prisoner every 15 minutes. The jail also had the capacity to video monitor a prisoner constantly but it was not clear if that was done.

Cameron Lindsay, a former warden who ran three US prisons, said the death was a "shocking failure."

He said: "Unequivocally, he should have been on active suicide watch and therefore under direct and constant supervision."

A medical examiner car is seen outside New York Presbyterian-Lower Manhattan Hospital, Credit: Reuters

Brad Edwards, who represents almost two dozens alleged victims of Epstein, said: "The fact that Jeffrey Epstein was able to commit the selfish act of taking his own life as his world of abuse, exploitation, and corruption unraveled, is both unfortunate and predictable. This is not the ending anyone was looking for."

He added: "The victims deserved to see Epstein held accountable, and he owed it to everyone he hurt to accept responsibility for all of the pain he caused."

Mr Edwards said he hoped police investigations into associates of Epstein would continue, and urged people to come forward with information. He said the the victims will "not stop in their pursuit of finality and justice."

Julie Brown, the Miami Herald journalist, who was at the forefront of investigations into Epstein, said: "It might open up the case even more because there might be people not as afraid to talk now. How many people are going to stand up now and finally speak up?"

Epstein was arrested on July 6, and had pleaded not guilty to charges of sex trafficking involving dozens of underage girls as young as 14, from at least 2002 to 2005.

In a statement Epstein's legal team said: "We are enormously sorry to learn of today’s news. No one should die in jail.

"We cannot confirm rumours as to his cause of death, and we trust that the US Attorney’s Office, and the US Marshals, will thoroughly investigate the circumstances of today’s tragedy."