Unfamiliar with the sounds of people doing productive work, the US Senate made desperate 911 calls reporting gunfire, and at least one staffer left the building by gurney, having suffered a panic attack. Sploid reports:

The entire Capitol complex had been in lock down since about 10:30 a.m. when police received reports of shots fired. The Senate had been in session at the time of the incident. the House had already snuck of for the first official "summer Friday" of the year, except for the House Intelligence Committee.

At around 11:00 a.m. an email was sent out by the U.S. Capitol police:

The US Capitol Police are continuing to investigate the report of gunshots in the Rayburn House Office Building. The Rayburn Building and garages are shut down at this time. The Longworth and Cannon Office Buildings and other garages are not affected. The Capitol Building is open for above ground access but the tunnels remain closed. As soon as the police have completed clearing the garage levels, they will begin search the remainder of the Rayburn Building beginning on the top floor and working down.

"It's a little unsettling to get a Blackberry message put in front of you that says there's gunfire in the building," said Rep. Peter Hoekstra.

And naturally, given the relative likelihoods of murderous rampages versus honest labour in the halls of the US government, the lawmakers jumped to the obvious conclusion. That they were wrong is truly a tragedy for our age.

It now appears that the source of the shots that rang throughout the garage at the Rayburn building was actually a pneumatic hammer being used to repair an elevator.