Mascheroni and his wife, Marjorie Roxby Mascheroni, pleaded guilty in 2013 to offering to help develop a nuclear weapon for Venezuela through dealings with an undercover FBI agent posing as a representative of the Venezuelan government. The FBI had seized computers, letters, photographs, books and cellphones from the couple's Los Alamos home. According to a 22-count indictment, Mascheroni told the undercover agent he could help Venezuela develop a nuclear bomb within 10 years and that Venezuela would use a secret, underground nuclear reactor to produce and enrich plutonium, and an open, aboveground reactor to produce nuclear energy.