The masked gunman who stalked and killed UnitedHealthcare CEO Brian Thompson outside a Manhattan hotel used ammunition emblazoned with the words “deny,” “defend” and “depose,” a law enforcement official said Thursday.

New clues are emerging in the hunt for the masked gunman who stalked and killed UnitedHealthcare CEO Brian Thompson, including possible leads about his travel before the shooting and a message scrawled on ammunition found at the crime scene.

The man accused of killing the head of one of the biggest U.S. health insurance companies is fighting being sent to face murder and other charges in New York City, where the attack happened.