A Wisconsin pharmacist told police he tried to ruin hundreds of doses of coronavirus vaccine because he felt the medicine wasn’t safe, a prosecutor said Monday.

Steven Brandenburg was arrested last week after an investigation into the 57 spoiled vials of the Moderna vaccine, which officials say contained enough doses to inoculate more than 500 people.

“He’d formed this belief they were unsafe,” Ozaukee County District Attorney Adam Gerol said during a virtual hearing. He added that Brandenburg was upset because he was in the midst of divorcing his wife, and an Aurora employee said Brandenburg had taken a gun to work twice.

Gerol didn’t explain why Brandenburg thought the vaccine wasn’t safe.

He has been fired and charges are pending while the FBI and U.S. Food and Drug Administration investigate.