WHAT WE KNOW ABOUT SUSPECTED SUBWAY BOMBER

U.S. Capitol evacuated after false alarm

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Police and other officials stand outside the US Capitol and the Capitol Visitor Center after the building was evacuated due to reports of a fire in Washington, DC, May 26, 2015. No smoke or fire were found and people were allowed to re-enter. (SAUL LOEB/AFP/Getty Images)

Police and other officials stand outside the US Capitol and the Capitol Visitor Center after the building was evacuated due to reports of a fire in Washington, DC, May 26, 2015. No smoke or fire were found and people were allowed to re-enter. (SAUL LOEB/AFP/Getty Images)

WASHINGTON (CNN) — The U.S. Capitol was evacuated briefly on Tuesday after an alarm went off in the Capitol Visitor Center.

Congress is on a week-long Memorial Day recess, so the House and Senate were not in session. Hundreds of staff, reporters and tourists, cooled their heels outside for more than an hour during the evacuation. Tour guides, who sport red blazers, took off their jackets and waited patiently in the shade of trees on the East front lawn, just a few hundred yards from the entrance to the building.

“U.S. Capitol Police & D.C. Fire are continuing to investigate the cause of an audible alarm. The U.S. Capitol Building and the U.S. Capitol Visitor Center are being evacuated due to the audible alarm,” the spokeswoman for the Capitol Police told reporters during the evacuation, adding that “there are no signs of smoke or fire.”

The false alarm comes two days after police discovered a pressure cooker emitting a gas smell in a vehicle near the annual Memorial Day concert outside the Capitol. Multiple federal and local law enforcement agencies responded to the scene over the weekend, but found nothing hazardous. The owner was taken into custody and later apologized to the local NBC affiliate station, saying he used the device in his food truck. Pressure cookers were used to create bombs used in the Boston Marathon attack in 2013.

The U.S. Capitol Police have come under criticism recently for their handling of a gyrocopter that landed on the West front lawn of the Capitol. The pilot of that vehicle wanted to deliver a political message and didn’t have any weapons with him. But his ability to fly undetected in restricted airspace and land without law enforcement alerting members and staff about a potential threat prompted key committee leaders to insist on a review of procedures.

During Tuesday’s incident, multiple email alerts were sent to staffers from the Capitol Police updating them on the situation.

“The U.S. Capitol Building situation has been resolved,” according to the final such message, which did not say what triggered the alarm, but told staffers to return to their offices.