(CNN) — Workers at the US Centers for Disease Control and Prevention have been told to return to the office September 15 – a little over a month after a gunman attacked the agency’s Atlanta campus, firing almost 500 shots and killing a police officer before dying of a self-inflicted gunshot wound.

The push for workers to return to the office was shared in an email to staff, a Health and Human Services spokesperson confirmed. The announcement comes just weeks after the August 8 attack left CDC staff reeling, with one staffer saying employees felt like “sitting ducks” as the shooter unloaded hundreds of bullets, around 200 of which struck six CDC buildings, leaving bullet holes in windows.

Employees, who were preparing to leave for the weekend, say they took cover under their desks as

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