In a flash, a dreary Monday morning turned to chaos, with SWAT teams running through the neighborhood, fully armed. Helicopters circled over America's shipbuilders at the Naval Sea Systems command in Washington, D.C., as bullets targeted the innocents just reporting for another day at work.
D.C. Metro police said they got their first call of multiple victims down at 8:20 a.m. By then, a security guard on the first floor of the Navy Sea Systems Command Center, the so-called “Building 197,” was hit.
And the gunman was on the upper floors apparently shooting down from atrium walkways into the open core of the five-story building, blasting away at the food courtyard below.
“Right after I paid for my breakfast, I heard three gunshots, ‘pow pow pow,’ straight in a row,” said Patricia Ward, a Navy Yard employee. “A few seconds later, there were four more gunshots and all the people in the cafeteria, we all panicked. We were trying to decide which way we were going to run out.”
These shots triggered a full-scale panic, an all-out rush for the exits, in a building where 3,000 military and civilian personnel work.
“A few of us just ran out the side exit,” said Ward. “We saw a security guard and she told us to run to shelter. She had a gun drawn and someone had pulled the fire alarm. That’s when I heard the police.”
Todd Brundidge and Terrie Durham were both on the third floor trying to escape the mayhem when they stepped directly into the gunman's sights.
“As we were exiting the back door, we noticed him down the hall, he stepped around the corner and we heard shots,” said Brundidge. “And as he came around the corner, he aimed his gun at us and he fired at least two or three shots. And we ran downstairs to get out of the building.”
“We could see him with the rifle and he raised and aimed at us and he fired and he hit high on the wall,” said Durham.
By 9:33 a.m., the first ambulances rushed victims to hospitals. And some victims were scooped off the roof, bravely airlifted to safety by circling helicopters. An ambulance with a police escort carried a D.C. patrolman who shot it out with the gunman.
At 9:45 a.m., the FAA stopped all flights in and out of Reagan National Airport. And back in the building, EMTs struggled to safely remove the injured.
Only later would police realize the toll -- 12 innocents dead, and 8 wounded in all.
Finally, at 12:14 p.m., police announced they had fatally shot the gunman.
The Navy Yard stayed on lockdown for more than 6 hours with survivors told to hide in place. Some barricaded themselves in top secret, secure closets, others under their desks.
Seven hours after the first shots were fired, at 3:15 p.m., the Capitol was locked down and the Washington Nationals called off their night Major League Baseball game, as rumors and reports swirled of multiple gunmen.
At 4:24 p.m., the FBI finally released the dead suspect's name: Aaron Alexis. But it wasn't until 10:19 p.m. that police felt confident that Alexis acted alone.
Military records showed Alexis was in the Navy from May 2007 to January 2011, serving at a Naval air station in Fort Worth, Texas.
Sources told ABC News that he also may last have worked as a civilian IT contractor for the Navy, and had a valid security clearance that allowed him on campus.
Photos of Alexis fit the description of eyewitnesses who described him as a steely-eyed killer, randomly gunning down whoever was in front of him, until he was shot and killed by police. But those reports collide with accounts of people who called him a friend.
“He has a gun, but I don’t think he’s that stupid,” said Nutpisit Suthamtewakul, owner of Happy Bowl Thai. “He didn’t seem aggressive to me.”
“It’s so night and day to me right now,” said Melinda Downs. “It’s just not even in his character.”
But ABC has learned Alexis had a history of disturbing behavior and brushes with the law. He was arrested in September 2010 in Fort Worth, accused of recklessly discharging a firearm into a neighbor's apartment. No one was injured and Alexis told police the gun accidentally went off when he was cleaning it.
And in May 2004, in Seattle, Alexis confessed to shooting out the tires of another man's car in an incident he described as “an anger-fueled blackout,” according to the Seattle Police Department. Alexis’ father told police “His son had experienced anger management problems that the family believed associated with PTSD.” He confirmed that his son “was an active participant in the rescue attempts of Sept. 11, 2001.”
Officials have found no evidence pointing to terrorism. A prime theory is that Alexis had a grudge against the Navy.
This is the fourth mass shooting this year with more than five people killed. And the 19th since President Obama took office in 2009. The president, who was marking the five-year anniversary of the financial crisis, opened his remarks with some all too familiar words.
“Today they faced the unimaginable violence that they wouldn't have expected here at home,” he said. “We will do everything in our power to make sure whoever carried out this cowardly act is held responsible. “In the meantime, we send our thoughts and prayers to all at the Navy Yard who have been touched by this tragedy.”
Late into the night, the FBI blocked off a Brooklyn, N.Y., street where they questioned Alexis’ parents. Agents were still looking at not just how, but why, this Monday morning tragedy ruined so many lives.