WASHINGTON -- As much as anything else, it was uncertainty that residents and workers in the most secure city in America wrestled with after they learned of a shooting rampage Monday morning at the military complex at the Navy Yard about a mile from the U.S. Capitol Building.
Many in Washington were on edge and wary as they scanned multiple and conflicting reports on social media and in news accounts about the number of wounded and dead -- and the number of shooters and whether they remained at large.
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Many wondered openly who was behind the attack, and how it could happen at the Naval Sea Systems Command, which D.C. Delegate Eleanor Holmes Norton called one of the most secure sites in the city.
Wayne Wilson, a civil engineer who works at the U.S. Department of Transportation a block from the site, heard and saw the response unfold -- the sirens blaring, the injured being taken away on gurneys.
What bothered him, he said, "was the uncertainty, as far as the proximate danger and the ease of its happening."
Near the White House, Justice Department attorney Starling Marshall, who moved here from Manhattan, said she couldn't help thinking about the 9/11 terrorist attacks and how the families of Monday's victims must feel.
She said her first thought was about how she had just gone through "active shooter" training by U.S. Marshals -- "and I thought 'I hope they had had the same training at the Navy Yard.' "
The uncertainty was evident in President Barack Obama's statement condemning the "cowardly act," but stopping short of defining it as crime or terror.
It also showed in the confusion on Capitol Hill.
The Senate canceled its session Monday and put its half of the Capitol Building on lockdown, while the House, which doesn't return until Tuesday, left its half open, allowing tourists to wander the halls.
Members of Congress, including Long Island representatives, condemned the shooting as they awaited more information.
Rep. Peter King (R-Seaford), a House Intelligence Committee member, usually gets a quick read on what's going on. But he said, "I just don't know. It could be one madman. It could be an anti-military plot."
It wasn't only official Washington that was affected.
The blocks around the shooting scene were roped off and neighbors were told to stay inside as the investigation continued.
Donald Holman, who works in crowd control at Washington Nationals baseball games, emerged Monday afternoon from the Navy Yard metro stop to go to the ballpark for Monday night's game -- which later would be postponed.
"Listening to the news, you don't know what's going on. But we have to come in," he said.
A cashier at a House cafeteria said, "You wake up in the morning to go to work -- and you just never know. I feel really bad for those people and their families."