About 8:15 a.m.

Aaron Alexis, a 34-year old computer contractor who had been discharged from the Navy in 2011 after a gun incident, opens fire in Building 197, according to authorities. Alexis shoots and kills security officer using a Remington shotgun he brought into the facility. He takes officer's handgun.

8:22 a.m.

An “active shooter team” of uniformed D.C. officers enters the building while shots are being fired. A series of firefights end with Alexis dead. Alexis was an hourly employee working on a subcontract with Hewlett-Packard. He had been given an access card that would have allowed entry to the building.

Shortly thereafter

The Navy Yard and several schools and nearby offices are locked down. Police fear that others might be involved.

3 p.m.

Many lockdowns are lifted.

About 4:30 p.m.

Authorities report that there are 13 fatalities, including Alexis.

10 p.m.

Mayor Vincent C. Gray says an additional eight people have been injured, including three shooting victims.