A union representing workers at the CDC said the incident was not random and “compounds months of mistreatment, neglect, and vilification that CDC staff have endured.”

As he grappled with those issues, sources said, White had become increasingly fixated on the COVID-19 vaccine as a source of his grievances. Several Kennesaw residents who knew the 30-year-old suspected shooter told ABC News they had heard White express similar angry and conspiracy-minded sentiments.