Guards in Jeffrey Epstein’s unit were working “extreme overtime” in the hours before his death, leaving gaps in his supervision, US media report.
The Department of Justice and the FBI have both launched investigations into Epstein’s death amid questions surrounding the circumstances.
Epstein, 66, was denied bail and faced up to 45 years in prison on federal sex trafficking and conspiracy charges.
A post mortem examination into Epstein’s death was performed Sunday.
New York City’s chief medical examiner, Dr Barbara Sampson, said that more information is needed before the cause of death is determined.
Dr Sampson said that a city medical examiner conducted the examination on Sunday while a private pathologist observed, at the request of Epstein’s representatives.
Corrections officers at New York’s Metropolitan Correctional Center had been forced to work overtime to make up for staffing shortages, according to US media.
One of the corrections officers was reportedly on his fifth straight day of overtime shifts, while another guard had been forced to work overtime, Serene Gregg, president of the American Federation of Government Employees Local 3148, told the Washington Post.
“If it wasn’t Mr Epstein, it would have been somebody else, because of the conditions at that institution,” she told the newspaper.
“It wasn’t a matter of how it happened or it happening, but it was only a matter of time for it to happen. It was inevitable. Our staff is severely overworked.”
Ms Gregg said she did not know the details of the investigation but that she has long complained about the work conditions at the facility.
The guards failed to follow several protocols leading up to Epstein’s death, according to the New York Times.
Epstein, who had been placed on suicide watch after his apparent suicide attempt last month, was supposed to have a cellmate and checked in on by a guard every 30 minutes. Mr Epstein was reportedly left alone early Saturday after his cellmate was transferred.
On Monday, two French government ministers also called for an investigation into Epstein, saying a US probe into the accused child sex trafficker had revealed links between Epstein and France.
What happens to the case against him?
Epstein was arrested on 6 July on new sex-trafficking charges. The indictment alleged that he paid girls under the age of 18 to perform sex acts at his Manhattan and Florida mansions between 2002 and 2005.
According to the charges – which Epstein denied – the girls, some as young as 14, were given hundreds of dollars for sex acts.
Hundreds of pages of court documents unsealed on Friday – one day before Epstein’s death – included new details of the sexual abuse claims against the multimillionaire, including allegations by a woman that she was forced to have sex with Epstein’s powerful friends.
Without Epstein to stand trial, legal experts told BBC’s US affiliate CBS News that federal prosecutors will likely dismiss the criminal case against Epstein.
Lisa Bloom, an attorney for several women who claim they were abused by Epstein, told CBS that she plans to file civil litigation against Epstein’s estate.
Attorney General William Barr said he was “appalled” to learn Epstein had died.
“Mr Epstein’s death raises serious questions that must be answered,” Mr Barr said on Monday, adding that he has demanded a “thorough” investigation.
What questions remain?
The death of the high-profile financier in such circumstances spurred a flurry of unsubstantiated conspiracy theories online.
But without the results from the post mortem examination, questions still loom regarding the precise cause of Epstein’s death.
How conspiracy theories spread after financier’s death
A city official told the New York Times that Dr Sampson is “confident” the cause of death is suicide by hanging, but she is awaiting further information from law enforcement before announcing the ruling.
Revelations that Epstein was left unsupervised and without a cellmate after an apparent suicide attempt in July has also raised questions.
Epstein was reportedly placed on suicide watch after being found unconscious in his cell with injuries to his neck, an incident that officials were investigating as a possible suicide or assault.
Who is Jeffrey Epstein?
Born and raised in New York, Epstein worked as a maths and physics teacher in the mid 1970s before moving into finance, creating his own firm: J Epstein and Co.
The company reportedly managed assets of clients worth more than $1bn (£800m). Epstein soon began spending his fortune – including on a mansion in Florida, a ranch in New Mexico, and reputedly the largest private home in New York.
But the specifics of Epstein’s work – including his client list – remained largely shrouded in secrecy. Reports of Epstein’s actual wealth varied, with his Virgin Islands-based firm generating no public records.
The hedge fund manager was better known for his famous circle of friends and associates. Epstein was tied to US President Donald Trump, Prince Andrew, actor Kevin Spacey and high-profile lawyer Alan Dershowitz.
He first came under scrutiny from law enforcement in 2005, when the parents of a 14-year-old girl told police in Florida that Epstein had molested their daughter at his Palm Beach home. A police search of the property found photos of girls throughout the property.
But prosecutors forged a deal with the financier in 2008 and Epstein avoided federal charges – which could have seen him face life in prison. Instead, he received an 18-month prison sentence, during which he was able to go on “work release” to his office for 12 hours a day, six days a week. He was released on probation after 13 months.