The warden and the head of the US Bureau of Prisons have been reassigned. Two employees accused of sleeping on the job and falsifying records have been placed on administrative leave.

Now, roughly 15 employees at the Metropolitan Correctional Centre where Jeffrey Epstein killed himself in his jail cell have been subpoenaed as the criminal investigation into the events around his suicide intensifies, according to a prison official and a person with knowledge of the matter.

The subpoenas, issued in recent days by federal prosecutors in Manhattan, are the latest sign of the heightened scrutiny over the suicide of the high-profile detainee at the chronically understaffed federal jail.

The US attorney general William Barr, whose Justice Department oversees the Bureau of Prisons, has complained about “serious irregularities at this facility”.

On Wednesday he went further, telling reporters in Dallas: “Unfortunately, there have been some delays because a number of the witnesses were not cooperative.”

Jeffrey Epstein: Controversies surrounding paedophile billionaire Show all 9 1 /9 Jeffrey Epstein: Controversies surrounding paedophile billionaire Jeffrey Epstein: Controversies surrounding paedophile billionaire Jeffrey Epstein in court Billionaire financier Jeffrey Epstein attends court as he pleads guilty to solicitation and procuring a person under the age of 18 for prostitution, 2008 Zuma/Rex Jeffrey Epstein: Controversies surrounding paedophile billionaire Jeffrey Epstein in court Billionaire financier Jeffrey Epstein pleaded guilty in 2008 to felony solicitation and procuring a person under the age of 18 for prostitution. He was sentenced to 18 months in jail. Epstein, allegedly paid several girls under the age of 18 in return for naked massages at his Palm Beach, Florida estate Zuma/Rex Jeffrey Epstein: Controversies surrounding paedophile billionaire Jeffrey Epstein's car Jeffrey Epstein is whisked away from the Palm Beach County jail in a black car shortly after 6am on 22 July 2009. Epstein left the jail through the sally port, where prisoners are brought in, rather than through the main doors where prisoners are routinely released Zuma/Rex Jeffrey Epstein: Controversies surrounding paedophile billionaire Jeffrey Epstein's mugshot Billionaire Jeffrey Epstein's mugshot, taken after he was indicted for soliciting a prostitute on 26 July 2006. Beginning in mid-March 2005, Epstein became the target of a sexual battery probe conducted by the Palm Beach Police Department, according to the affidavit, which alleges that Epstein paid a series of underage girls to engage in sexual activity with him. In a 2002 New York magazine profile of Epstein, Donald Trump called the moneyman a 'terrific guy' who 'likes beautiful women as much as I do, and many of them are on the younger side.' Epstein, who reportedly runs a multibillion-dollar investment fund, travels in his own Boeing 727 (upon which he has transported Bill Clinton to Africa) and owns a 45,000-square-foot mansion on Manhattan's Upper East Side Palm Beach County Sheriff's Department Jeffrey Epstein: Controversies surrounding paedophile billionaire Jack Goldberger, Jeffrey Epstein's attorney Jeffrey Epstein's attorney, Jack Goldberger, talks with reporters gathered outside the Palm Beach County jail on 22 July 2009 after Epstein was whisked away from the jail in a black car Zuma/Rex Jeffrey Epstein: Controversies surrounding paedophile billionaire Jeffrey Epstein Florida Police department sexual offenders database picture of Jeffrey Epstein taken in 2013 Jeffrey Epstein: Controversies surrounding paedophile billionaire Jeffrey Epstein's mansion His Palm Beach mansion in Florida Google Jeffrey Epstein: Controversies surrounding paedophile billionaire Jeffrey Epstein's island The private Caribbean island, Little St James is part of the US Virgin Islands NBC News Jeffrey Epstein: Controversies surrounding paedophile billionaire Jeffrey Epstein's island The private Caribbean island, Little St James is part of the US Virgin Islands NBC News

The suicide of Epstein, 66, a wealthy financier accused of sexually abusing dozens of girls, has put pressure on Mr Barr to explain how such a prominent defendant was left unsupervised long enough to kill himself.

It was unclear which employees had received subpoenas, but Mr Barr said on Wednesday that a number of witnesses at the jail were requiring union representation and lawyers before they would agree to interviews.

Eric Young, president of the union that represents federal prison workers, disputed Mr Barr’s claim that jail employees had been uncooperative. He said the Justice Department had been unwilling to grant immunity to workers.

“The Justice Department would like employees to waive away their minimum constitutional right to representation,” Mr Young said in an interview on Thursday. “That’s what they consider to be a cooperative employee.”

The two staff members in the special housing unit where Epstein was held — 9 South — are accused of falsely recording in a log that they had checked on Epstein every 30 minutes, as was required.

But Epstein, who had been removed from suicide watch after apparently trying to kill himself on 23 July, had not been checked on for about three hours, several law enforcement and prison officials with knowledge of the matter have said.

The subpoenas seek testimony from the jail employees are part of an inquiry being conducted by the FBI, prosecutors with the Southern District of New York and investigators from the New York office of the Department of Justice’s inspector general, said a person with knowledge of the investigation, who asked to remain anonymous because he was not authorised to speak on the matter.

It was unclear whether the subpoenas also sought records or other materials.

The New York City medical examiner determined that Epstein’s death was a suicide by hanging.

Trump defends promoting Epstein death conspiracy theory

Still, that has not quashed unfounded conspiracy theories that claim other people may have played a role in silencing Epstein, whose social circle included celebrities, academics and powerful politicians.

A decade ago, Epstein served 13 months in a Florida jail and registered as a sex offender after pleading guilty to state prostitution charges under a highly criticised agreement that, at the time, shielded him from federal prosecution.

He was arrested last month by FBI agents and New York police detectives at Teterboro Airport in New Jersey and charged with federal sex trafficking following renewed interest in his case.

The Justice Department has announced high-level staffing changes since Epstein’s suicide.

The acting director of the Bureau of Prisons, Hugh Hurwitz, was reassigned Monday, and the warden of the Manhattan jail, Lamine N’Diaye, was transferred to an office in Philadelphia.

The Metropolitan Correctional Centre and other federal prisons across the country have been dealing with rising levels of violence and other safety problems as the Trump administration, in its quest to shrink the government, has curtailed prison hiring, according to an investigation by The New York Times last year.

Some prisons, including the Manhattan jail, have been so pressed for guards that they have forced teachers, nurses, cooks and other support staff members to step in.

One of the staff members who was guarding Epstein when he died was not a regular correctional officer, but instead worked in the business office, according to three prison officials.

Staffing shortages existed before Trump took office, but a government-wide hiring freeze imposed just days into his administration pushed the Bureau of Prisons’ employment into free-fall.

Drone captures FBI raiding Jeffrey Epstein's Caribbean home

The freeze was lifted elsewhere in April 2017, but remained in place at the bureau for several more months.

The Bureau of Prisons employs 15,012 correctional officers nationwide, down from 16,623 in December 2016, according to data provided by the agency.

At the Manhattan jail, there are 111 officers, down from 137 at the end of 2016. There are currently 17 vacant positions for correctional officers at the jail, according to the Bureau of Prisons.

The last suicide at the Manhattan jail before Epstein’s was in 2006, according to the bureau.