The well-connected financier, 66, was found dead on Saturday while awaiting federal trial for sex trafficking.
The US Bureau of Prisons had already called his death an "apparent suicide" but that did not stop conspiracy theories from swirling.
President Donald Trump had suggested there may have been foul play.
The Department of Justice has launched an investigation into how Epstein was able to die in New York's highly secure Metropolitan Correctional Center (MCC).
Attorney General William Barr said officials have uncovered "serious irregularities" at the jail, which has housed other high-profile detainees such as Mexican drug baron El Chapo and fraudster Bernie Madoff.
He has also promised that Epstein will continue to be investigated in order to bring to justice any other possible conspirators.
Earlier this week, two prison guards were suspended and a warden temporarily reassigned from MCC amid widespread reports that 30-minute checks, required within Epstein's unit, were not carried out properly.
Epstein was discovered on the floor of his Special Housing Unit cell at about 06:30 (10:30 GMT) local time on Saturday.
It came after an earlier suicide attempt on 23 July that saw Epstein temporarily transferred to the special suicide watch wing of the jail.
On Tuesday the New York Times reported that guards in the Special Housing Unit had allegedly fallen asleep on the night of Epstein's death.
One guard was working a fifth straight day of overtime shifts, it was reported, while another was forced to work mandatory overtime that night.
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