The FBI and U.S. Inspector General's office will investigate how Jeffrey Epstein died in an apparent suicide Saturday, while the probe into sexual abuse allegations against the well-connected financier remains ongoing, officials said.

Epstein, the well-connected financier accused of orchestrating a sex-trafficking ring, had been taken off suicide watch before he killed himself in a New York jail, a person familiar with the matter said.

Attorney General William Barr said he was "appalled" to learn of Epstein's death while in federal custody. The FBI and the Department of Justice's Office of the Inspector General will investigate, he said.

"Mr. Epstein's death raises serious questions that must be answered," Barr said in a statement.

Epstein was found unresponsive in his cell Saturday morning at the Metropolitan Correctional Center, according to the Federal Bureau of Prisons. Fire officials received a call at 6:39 a.m. Saturday that Epstein was in cardiac arrest, and he was pronounced dead at New York Presbyterian-Lower Manhattan Hospital.

Epstein, 66, had been denied bail and faced up to 45 years behind bars on federal sex trafficking and conspiracy charges unsealed last month. He had pleaded not guilty and was awaiting trial on accusations of sexually abusing dozens of underage girls.

The federal investigation into the allegations remains steadfast, U.S. Attorney Geoffrey Berman said. He noted in a statement Saturday that the indictment against Epstein includes a conspiracy charge, suggesting others could face charges in the case.

Lisa Bloom, a lawyer representing some of Epstein's alleged victims, tweeted after his death that civil cases will proceed against his estate. She added that her clients would have liked him to live to "face justice."

She later added a statement from an alleged victim who says, "I will never have a sense of closure now."

From one of my Jeffrey Epstein victim clients this morning. <a href="https://t.co/8gRozyQPMP">pic.twitter.com/8gRozyQPMP</a> —@LisaBloom

Previous injuries self-inflicted?

Epstein had been placed on suicide watch and given daily psychiatric evaluations after an incident a little over two weeks ago in which he was found with bruising on his neck, according to the person familiar with the matter who wasn't authorized to discuss it publicly. It hasn't been confirmed whether the injury was self-inflicted or the result of an assault.

Epstein was taken off suicide watch at the end of July, the person said.

Police officers cover a medical examiner car outside New York Presbyterian-Lower Manhattan Hospital, where Epstein's body was transported before being moved to a medical examiner's office in New York City on Aug. 10. (Jeenah Moon/Reuters)

The Bureau of Prisons confirmed that he had been housed in the jail's Special Housing Unit, a heavily secured part of the facility that separates high-profile inmates from the general population. Until recently, the same unit had been home to the Mexican drug lord Joaquin "El Chapo" Guzman, who is now serving a life sentence at the so-called Supermax prison in Colorado.

Epstein's death raises questions about how the Bureau of Prisons ensures the welfare of high-profile inmates. In October, Boston gangster James "Whitey" Bulger was killed in a federal prison in West Virginia where he had just been transferred.

Nebraska Sen. Ben Sasse, a Republican member of the Senate Judiciary Committee, wrote Saturday in a scathing letter to Barr that "heads must roll" after the incident.

"Every single person in the Justice Department ... knew that this man was a suicide risk, and that his dark secrets couldn't be allowed to die with him," Sasse wrote.

Death a 'shocking failure'

Cameron Lindsay, a former warden who ran three federal lockups, said the death represents "an unfortunate and shocking failure, if proven to be a suicide."

"Unequivocally, he should have been on active suicide watch and therefore under direct and constant supervision," Lindsay said. "When you have an inmate as high profile as Epstein, it's absolutely imperative the warden set the tone with his or her leadership to ensure these kinds of incidents don't happen."

Epstein's removal from suicide watch would have been approved by both the warden of the jail and the facility's chief psychologist, said Jack Donson, a former prison official who worked for the Bureau of Prisons for more than two decades.

An attorney for Jeffrey Epstein, Marc Fernich, said in a statement that jailers at the Metropolitan Correctional Center failed to protect Epstein and to prevent the "calamity" of his death.

Fernich also said that reporters, plaintiffs' lawyers and court officials "should be ashamed of their behaviour" following Epstein's indictment. He said Epstein had "long since paid his debt to society" for his crimes.

Epstein was in detention while awaiting his trial, where he was reportedly taken off suicide watch. His trial was not expected to begin until next June. (New York state Division of Criminal Justice Services via Reuters)

Epstein's arrest last month launched separate investigations into how authorities handled his case initially when similar charges were first brought against him in Florida more than a decade ago. U.S. Labor Secretary Alexander Acosta resigned last month after coming under fire for overseeing that deal when he was U.S. attorney in Miami.

On Friday, more than 2,000 pages of documents were released related to a since-settled lawsuit against Epstein's ex-girlfriend by Virginia Giuffre, one of Epstein's accusers. The records contain graphic allegations against Epstein, as well as the transcript of a 2016 deposition of Epstein in which he repeatedly refused to answer questions to avoid incriminating himself.

Sigrid McCawley, an attorney representing some of alleged victims of Jeffery Epstein, speaks to reporters in front of a courthouse in New York on July 18 as a judge denied bail for Epstein. (Seth Wenig/The Associated Press)

Sigrid McCawley, Giuffre's attorney, said Epstein's suicide less than 24 hours after the documents were unsealed "is no coincidence." McCawley urged authorities to continue their investigation, focusing on Epstein associates who she said "participated and facilitated Epstein's horrifying sex trafficking scheme."

Accusers left angry

Other accusers and their lawyers reacted to the news with frustration that the financier won't have to face them in court.

"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," accuser Jennifer Araoz said in a statement.

In this Monday July 8, photo, lawyer Brad Edwards, centre, leaves federal court with his clients Michelle Licata, left, and Courtney Wild, right, after Epstein appeared for his arraignment in New York. Edwards said Epstein's death is 'not the ending anyone was looking for.' (Bebeto Matthews/The Associated Press)

Brad Edwards, a Florida lawyer for nearly two dozen other accusers, said that "this is not the ending anyone was looking for."

"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," Edwards said in a statement.

Epstein's arrest drew national attention, particularly focusing on a deal that allowed Epstein to plead guilty in 2008 to soliciting a minor for prostitution in Florida and avoid more serious federal charges. He was a registered sex offender, but had apparently evaded a requirement to check back regularly with New York police.

Federal prosecutors in New York reopened the probe after investigative reporting by The Miami Herald stirred outrage over that plea bargain.

His lawyers maintained that the new charges brought by federal prosecutors in New York were covered by the 2008 plea deal and that Epstein hasn't had any illicit contact with underage girls since serving his 13-month sentence in Florida.

Facilities at Little St. James Island, one of Epstein's properties, are seen in an aerial view, near Charlotte Amalie, St. Thomas, U.S. Virgin Islands, on July 21. (Marco Bello/Reuters)

Before his legal troubles, Epstein led a life of extraordinary luxury that drew powerful people into his orbit.

He socialized with princes and presidents and lived on a 100-acre private island in the Caribbean and one of the biggest mansions in New York. A college dropout, he became a sought-after benefactor of professors and scientists, donating millions of dollars to Harvard University and other causes.

Still, it was never entirely clear how the middle-class Brooklyn math whiz became a Wall Street master of high finance.

Wealthy entertained at NYC mansion

The somewhat reclusive Epstein splashed into the news in 2002 after a New York tabloid reported he had lent his Boeing 727 to ferry former president Bill Clinton and other notables on an AIDS relief mission to Africa.

Magazine profiles followed and established Epstein's reputation as a stealthy, yet exorbitantly successful, money man with a gilded social circle and a somewhat ascetic streak.

Vanity Fair in 2003 described him entertaining real estate tycoons, business executives and the scions of some of America's wealthiest families at his New York mansion — while also spending 75 minutes a day practicing yoga with a personal instructor and eschewing email, alcohol, tobacco and drugs.

His friends over the years have included Donald Trump, Prince Andrew and former Harvard law professor Alan Dershowitz.

But Epstein also enjoyed surrounding himself with women much younger than he, including Russian models who attended his cocktail parties and beautiful women he flew aboard his plane, according to the Vanity Fair profile.