The gunman who opened fire Friday at the US Centers for Disease Control and Prevention broke into his father’s safe to get the five firearms recovered at the scene, state investigators said Tuesday, as some CDC workers seeking answers and reassurance from leadership were left dissatisfied by a short agency-wide meeting about the shooting.

The FBI says more than 500 shell casings have been found around the scene of last week's shooting near the CDC headquarters in Atlanta. On Tuesday, authorities released the 911 call from the suspect's father following the shooting.

A search of Patrick Joseph White’s home revealed documents in which he indicated his discontent with the vaccine, they said.