The Associated Press is reporting that Nathan Safferstein, a counterintelligence agent for the Manhattan Project, has died.

Safferstein’s family told the AP that he died Tuesday, March 5 at his home in the Bronx. He had been suffering from an unnamed illness for some time.

As part of the program centered around creating the atomic bomb, Safferstein was trusted with some of the Manhattan Projects’ most precious secrets. The AP report states that Safferstein eavesdropped on Los Alamos laboratory scientists to ensure they weren’t leaking secrets about the program. He was also tasked with transporting sensitive material, such as uranium and top-secret messages.

Safferstein was reportedly a grocery store manager before being recruited into the Manhattan Project and stationed at Los Alamos. He followed the project all the way to the Pacific theater, where he was able to sign his initials to the atomic bomb dropped in Hiroshima. After the war, Safferstein returned to grocery store work. He went on to become president of a marketing company and later founded two companies.

(Image courtesy Michael Safferstein/AP)