Approximately 8:15 a.m.

1Aaron Alexis, wearing a backpack, enters Building 197 with a valid pass and key card.
2Law enforcement sources say he made his way to a fourth-floor bathroom and emerged with a shotgun.
Altered Remington 870 shotgun
34He begins firing his shotgun from the fourth floor, then goes down to the third floor and the lobby.

8:23 a.m.

Police receive report of gunshots at Navy Yard Building 197. A four-person active shooter team is assembled and reaches the Navy Yard in two minutes. Within six minutes, they are inside the complex.

8:28 a.m.

An e-mail goes out to Navy Yard workers telling them to "shelter in place."

8:30 a.m.

Seven minutes after the police received the call, the first units armed with AR-15 assault rifles hear shots and enter the building.

8:43 a.m.

Emergency responders are warned by officers in the building that there is an active shooter and several victims down.

At some point

Alexis kills a security guard in the lobby and takes the guard's 9mm handgun, according to law enforcement authorities. He drops the shotgun and begins firing with the handgun.
Beretta 9mm

8:55 a.m.

5As police units engage him, Alexis makes his way back upstairs to the third floor. Emergency responders report a D.C. police officer down on the third floor.

Approximately 9:20 a.m.

6Alexis is fatally shot in the head on the third floor by a D.C. police officer after "multiple engagements" with officers between 30 minutes and an hour after the first units arrived.
Building 197 was built in 1939 as a factory that made guns for battleships during World War II. It has housed the Naval Sea Systems Command since 2001.
Shooter enters building
Visitor entrance
Employee entrance
Requires badge
Rick MasonProgram management analyst
Mason told the Associated Press that a gunman was shooting from a fourth-floor overlook in the hallway outside his office. He said the shooter aimed at people in the first-floor cafeteria.
Assembles gun in fourth-floor bathroom
Shoots on Floors 4 and 3
Christopher MercerNavy captain
Mercer said he and colleagues slammed the door of his third-floor office shut as Alexis fired into Michael Arnold's office across the hall. Soon after, a bullet ripped through his door at shoulder height. “He set up camp right in front of my office,” Mercer said.
“He kept reloading and firing at cubicles. Later, when he came back, I could see his shadow through the glass pane in my door.” Alexis was killed in a firefight with police in the office next to Mercer's.
Shooter engages with responders
Shooter is killed
Gregory DadeHewlett-Packard employee
Dade and a colleague were in their second-floor office when they heard gunfire. They ran into the hall, inadvertently getting closer to the shooting. “We could smell the sulfur type of smell. You could just see it and smell it,” he said. They ran back to the office and locked the door.
Patricia Ward
At 8:15 a.m., Ward was standing at an ATM in first-floor atrium of Building 197 when she heard gunshots. She was on her way to breakfast in the cafeteria nearby.
Shooter in lobby
SOURCE: Staff reports. GRAPHIC: The Washington Post.