All CDC employees nationwide, except for essential on-site personnel, have been instructed to work remotely on Monday as Georgia investigators continue probing Friday's deadly active shooter incident near the agency's Atlanta headquarters, according to a letter obtained by ABC News.

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.