WASHINGTON (CNN) -- A fire alarm went off, as has happened before at the Washington Navy Yard. Terrie Durham wasn't sure if it was anything serious, or a drill.
Then office fire wardens came in and yelled for everyone to get out as fast as possible, and "that's when we started moving," she told CNN affiliate WJLA.
She and Todd Brundidge were part of a group that rushed into a hallway toward the exit. Then they saw a man with a rifle.
"We noticed him down the hall and he stepped around the corner and we heard shots," Brundidge told WJLA. What seemed like two or three seconds passed, and then "he aimed his gun at us and then he fired at least two or three shots."
The pair provided the first apparent eyewitness account of a suspect they described as a tall African American man accused by authorities of being one of possibly multiple attackers who killed at least 12 people at the heavily secured facility along the Anacostia River not far from the U.S. Capitol and just blocks from where baseball's Washington Nationals play.
Durham said the gunman was too far away to see his face, but "we could see him with the rifle and he raised and aimed at us and fired." The shots hit high on the wall, and the group she was with ran out of the building.
Navy Cmdr. Tim Jirus didn't see a gunman, but he witnessed the carnage.
He told CNN that he was in an alley outside Building 197 to help people get down the fire escapes. A worker from the building approached him to say he heard someone was shooting inside.
Then he heard more gunfire -- two shots that apparently came from the building. The man who stood three feet from him fell to the ground, bleeding from a head wound, "and that's when I ran," Jirus said.
"I never met him before in my life," said Jirus, who described himself as "lucky to be here."
He had not heard clear gunshots earlier, but this time, he was certain.
"In the alleyway with the amount of sound reverberating, you know exactly what it is, not to mention he's on the ground, bleeding," Jirus said.
The shootings that began around 8:20 a.m. set off chaotic scenes in the area, with the FBI and other law enforcement agencies converging in what seemed like a tidal wave of sirens and helicopters. On the street, workers from the huge Navy complex rushed out of the building."
Everybody was going down the stairs," Brundidge said in describing the pandemonium. "People were pushing. People were shoving. People were falling down. After we came outside, people were climbing the wall, trying to get out over the wall. ... It was just crazy."
Paul Williams, a program coordinator at a nonprofit that works with foster children, was heading to his office near the Navy Yard when he encountered what he described as a panic.
"I had my headphones in, so I didn't know what was going on," Williams, 29, told CNN. "I was listening to music, but I heard four rapid bangs---bang, bang, bang, bang."
At first he thought it was construction noise that has become common the area, but about 30 seconds later, he saw a rush of what looked like hundreds people coming towards him from the Navy Yard.
"I didn't know what was happening. I just ran with them," Williams said, adding that "everyone seemed scared. People were crying, people were being consoled and calling loved ones and family."
His assessment echoed what Brundidge had said: "It was crazy."
Brundidge said he "couldn't believe it."
"You know," he said, "you just go to work and you never think something like this is going to happen in your building."
CNN's Rene Marsh, Ashley Killough and Virginia Nicolaidis contributed to this report.
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