Authorities are investigating the in-custody death of a federal inmate who was found unresponsive Monday morning at the United States Penitentiary in Atlanta.

Few details have been released about the death of 31-year-old Robert Snipes, who was serving a six-year prison sentence for robbing a bank in Illinois.

Snipes was found unresponsive at the medium-security penitentiary about 9:15 a.m., officials said in a news release. Prison staff performed life-saving measures after finding the inmate. He was taken to the hospital, where he was pronounced dead.

Authorities have not released a cause of death in the case, but the FBI was notified, authorities said.

“No staff or other inmates were injured and at no time was the public in danger,” prison officials said in the release.

According to federal court records, Snipes robbed a bank branch inside a Chicago grocery store after slipping the teller a note implying that he had a bomb in his backpack. He later pleaded guilty and received a 72-month prison sentence.

In 2018, Snipes tried to appeal his guilty plea and subsequent conviction, but that appeal was dismissed.

No additional details about his death were released.

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