Jeffrey Epstein’s shocking death occurred at an ultra-secure federal lock-up where suicide is supposedly next to impossible.

Yet Epstein, 66, apparently managed to hang himself in his cell in the Special Housing Unit on the 9th floor of the federal Metropolitan Correctional Center at about 6:30 a.m. Saturday.

He had been on suicide watch there, presumably without access to a belt or shoelaces and closely monitored by guards, as is standard protocol, but was taken off the list sometime before Saturday, when he was found curled up and unresponsive.

One report said the watch was removed as recently as Thursday, but others claimed it had been in place only for about a week after the July 23 incident that left Epstein with bruises on his neck.

Jail spokesman Lee Plourde would not discuss when the watch status was removed or why, a step that would require a face-to-face evaluation and written justification, according to Bureau of Prisons policy.

Suicide at the jail, which serves mainly as a holding facility for about 765 men and women awaiting trial for federal crimes of all levels, is rare.

A review of published stories found only one such death in the past 21 years, the 1998 suicide of South Philadelphia drug kingpin Louis Turra, who reportedly hanged himself.

A handful of suicide attempts were also reported.

But life in the specialized units often involves inmates being watched by cameras in their cells and checked by guards almost constantly.

One former inmate, Uzair Paracha, who was held there for two years until 2005, wrote he was subjected to frequent strip searches, isolation from other prisoners, lights that were left on 22 or 23 hours per day.

He said guards “monitored us like lab rats.”

Before being convicted of supporting al-Qaida, Paracha was held mainly in the unit known as 10 South, a solitary confinement ward for the highest risk inmates, including 1993 World Trade Center bomber Ramzi Yousef, Ponzi king Bernard Madoff and drug lord Joaquin “El Chapo” Guzman.

Paracha also spent time in 9 South, where inmates like Epstein who are assigned to protective custody are housed. That floor has its own set of stringent security measures.

Attorney General William Barr was reportedly “livid” when he learned of Epstein’s death.

He said in a statement Justice Department’s Inspector General, as well as the FBI, are probing the matter.

“Mr. Epstein’s death raises serious questions that must be answered,” Barr said.

Others were outraged.

“We need answers,” tweeted U.S. Rep. Alexandria Ocasio-Cortez. “Lots of them.”

Tweeted former mayor Rudolph Giuliani: “What does the word suicide mean in the phrase suicide WATCH?”

“Who was watching? Did they fall asleep? Did the camera malfunction? Was there camera surveillance? Who was he about to implicate? This is very questionable. Committing suicide on suicide watch doesn’t happen.”

Even so, law-enforcement officials note that suicide is a leading cause of death behind bars.

In 2013, 34 percent of inmate deaths were due to suicide, according to a Department of Justice report.

And sex offenders are more likely than others to try to kill themselves.

“Pedophiles facing federal criminal charges are at high risk for suicide,” tweeted former Deputy Attorney General Rod Rosenstein.

“It happened in several of my Maryland cases when defendants were released on bail. Detained pedophiles require special attention. Stopping people from harming themselves is difficult.”