In Building 197, the bustling headquarters of the Naval Sea Systems Command in Washington, navy Captain Mark Vandroff was running a meeting. "I had a very routine day planned for myself," he said.
On the fourth floor, Commander Tim Jirus heard what sounded like muffled gunshots. After helping evacuate workers, he was in an alleyway when a maintenance worker told him the shooter was still in the building. As Jirus stood next to him, the worker was shot in the head. "I'm fairly certain he was dead," said Jirus, who ran for cover.
Employees described carnage at the naval administrative complex alongside the Anacostia River in southeast Washington. Thirteen people would die, including Alexis.
Although access was closely controlled, employees said, they did not have to pass through metal detectors. Workers first present their military ID cards to an armed security guard at the compound's entrance. To enter Building 197, they swipe the card over an electronic reader.
Programme manager Gary Humes said he was nearing the entrance when he heard a blast and saw people running out the door. He took shelter across the street in Building 201. He'd come to work a few minutes late. "I guess God was on my side on that one," Humes said.
Vandroff, manager of the navy's non-nuclear surface ships, was running a meeting in a third-floor conference room when he heard gunfire, looked up and saw two bullet holes in the wall near the ceiling. Everyone pushed tables against the doors, then hit the floor, he said.
Vandroff said they heard intermittent gunfire for about 40 minutes, until a police team checked their identities and cleared them to leave. His staff were safe, but a friend was killed. "I know I lost a friend today," he said. "I haven't processed that yet. I don't know how you process something like this. I count myself lucky to be out here."
The neighbourhood was locked down much of the day, with children sheltered in schools and flights suspended for a time at Reagan National Airport. A car park at the nearby baseball stadium was turned into a family meeting area.
Weary-looking employees straggled away from the complex, talking on mobile phones. Most did not want to comment.
Doug Hughes, who had locked himself and a co-worker inside an office on the first floor of Building 197, was on his way to the family area to meet his wife. He didn't know what he was going to say to her. "I'm just going to hug her," he said.