"Kennedy is directly responsible for the villainization of CDC's workforce through his continuous lies about science and vaccine safety, which have fueled a climate of hostility and mistrust," one ex-employee wrote, according to the Associated Press news agency.

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.