WASHINGTON (AP) — A worker at a federal prison in California has died and investigators are examining whether he was exposed to fentanyl shortly before his death, three people familiar with the matter told The Associated Press. Marc Fischer, a mailroom supervisor at the U.S.

Penitentiary in Atwater, California , died Friday after he reported feeling ill earlier, the people said. They said he was taken to a local hospital and was pronounced dead later in the evening. Investigators are examining whether he was exposed to a substance authorities believe was fentanyl while he screening mail at the prison, the people said.

The people could not publicly discuss details of the ongoing investigation and spoke to the AP on condition of anonymity. Fischer's cause of death remained unknown Saturday and it was unclear whether the potential exposure may have contributed. Briefly touching fentanyl cannot cause an overdose , and researchers have found that the risk of fatal overdose from accidental exposure is low.

In a statement, the Bureau of Prisons said an employee at the prison “began feeling unwell following an exposure to mail saturated in an unknown substance” and was pronounced dead after being rushed to the hospital. A second worker was taken to the hospital for observation after coming in contact with the mail and was later released, the agency said. “Our hearts are heavy as we extend our deepest condolences to the family, friends, and colleagues of our fallen Bureau empl.