At least 13 people are dead and 14 injured after a gunman opened fire at the Washington Navy Yard in Washington D.C. this morning. Parts of the capital were in lock down as authorities worked to contain the panic. The shooting represents the single worst loss of life in the capitol since 1982.

The violence began just after 8 a.m. Employees were met with a scene of mass confusion as the sound of gunshots broke out in the halls of the Naval Sea Systems Command headquarters. According to officials, the gunman drove onto the base and began firing as soon as he approached building 197, killing a police officer. After he made his way into the building, he took aim from a floor overlooking an atrium and fired on the employees eating breakfast below.

The shooter, identified by the FBI as Aaron Alexis, was among the 13 dead. Alexis was a military contractor and a resident of Fort Worth. Initially, authorities were on the lookout for two suspects, but one has since been cleared. The other, described by D.C. Police Chief Cathy L. Lanier in a series of news conferences, was a black man in his late 40s with gray sideburns. He, along with the man who was cleared, came under suspicion when they were seen on surveillance videos. By evening, authorities said they believed only one gunman was involved.

Three weapons were found on Alexis: an AR-15 semiautomatic rifle, a shotgun, and a semiautomatic pistol. Officials are currently working to establish a motive for the attack.