The man accused of killing a police officer while shooting at the U.S. Centers for Disease Control and Prevention (CDC) headquarters in Atlanta had previously been reported to police for suicidal thoughts and launched the deadly attack with his father’s weapons to send a message against COVID-19 vaccines,

Documents found in a search of the home where Patrick Joseph White lived with his parents “expressed the shooter’s discontent with the COVID-19 vaccinations,” authorities said.

CDC security guards stopped White from driving into the campus on Friday before he parked near a pharmacy across the street and opened fire from a sidewalk. The bullets pierced “blast-resistant” windows across the campus, pinning employees down during the barrage. More than 500 shell casings were recovered, the GBI said.