Prison officials were already investigating after the 66-year-old financier was found unconscious in his Manhattan Correctional Center jail cell July 23 after a possible suicide attempt.
The incident prompted his move to a suicide watch unit, people familiar with the matter told The Wall Street Journal last month.
Epstein had been taken off suicide watch before he killed himself, the Associated Press reported, citing a person familiar with the matter.
Those demanding answers included Rep. Alexandria Ocasio-Cortez, D-N.Y., who tweeted, "We need answers. Lots of them."
Rep. Matt Gaetz tweeted he agreed with AOC.
"Chairman @RepJerryNadler should prioritize a Judiciary investigation into how Jeffrey Epstein died in federal custody (in Nadler’s own neighborhood!) over the Kavanaugh confirmation (which already happened), and the Russia hoax (which never happened)," Gaetz said.
Bureau of Prisons officials ruled Epstein’s death an apparent suicide, saying he was found unconscious in his cell in the downtown Manhattan facility around 6:30 a.m.
“Staff requested emergency medical services (EMS) and life-saving efforts continued,” Bureau of Prisons spokesman Lee Plourde said. “Mr. Epstein was transported by EMS to a local hospital for treatment of life-threatening injuries, and subsequently pronounced dead by hospital staff. “
Epstein was being held at MCC without bail after his arrest July 6 on charges of sexually abusing young girls in New York and Florida.
Former Deputy Attorney General Rod Rosentein said on Twitter Saturday that pedophiles facing federal charges are at high risk for suicide.
"Detained pedophiles require special attention," he said. "Stopping people from harming themselves is difficult."
In the July incident, Epstein was found on the floor of his cell with bruising around his neck, according to The New York Times.
A law enforcement official told the paper at the time his injuries were not serious and another person briefed on the matter said officials had not ruled out the possibility he had been assaulted by another inmate or had staged the incident.
His cell-mate then was Nicholas Tartaglione, a former police officer facing murder charges, the Times reported. A lawyer for Tartaglione, Bruce Barket, of New York, said at the time that “any insinuation that he had assaulted Mr. Epstein is a complete and utter fabrication.”
Inmates in federal custody who are placed on a suicide watch are kept under constant observation by staff or trained inmate observers, according to federal regulations.
The observers are required to document what they see in a log book.
According to the regulations, an inmate can be moved from suicide watch when it is determined by a psychologist that the inmate “is no longer at imminent risk for suicide” or has been transferred to a hospital.
Epstein and Tartaglione’s cell was in an area of MCC called 9 South, a special unit apart from the facility’s general inmate population, Bloomberg News reported last month.
On 9 South Epstein and other inmates are allowed to leave their cell for an hour of recreation each day and to confer with lawyers, The Wall Street Journal reported last month.
The paper said Epstein spent much of his time in the bottom bunk of a windowless 8-by-8 foot cell.
MCC inmates population numbers about 800. Most are awaiting trial.
Prominent inmates have included Cesar Sayoc, who was just sentenced to 20 years in prison for sending bombs to prominent Democrats, drug lord Joaquin “El Chapo” Guzman and former Trump campaign manager Paul Manfort.