Capitol Police sent this alert out to Congressional offices, with a “Shelter in Place!” subject line:
SHELTER IN PLACE. Gunshots have been reported on Capitol Hill requiring all occupants in all House Office Buildings to shelter in place. Close, lock and stay away from external doors and windows. Take annunciators, Go Kits and escape hoods; and move to the innermost part of the office away from external doors or windows. If you are not in your office, take shelter in the nearest office, check in with your OEC and wait for USCP to clear the incident. No one will be permitted to enter or exit the building until directed by USCP. All staff should monitor the situation. Further information will be provided as it becomes available.