A mass shooting at Naval Sea Systems Command in Washington D.C. Monday morning left 13 people dead and several wounded.
The suspected gunman, 34-year-old Aaron Alexis of Forth Worth, Texas, is among the dead and authorities are looking for a possible second shooter described as a black man in his 40s with gray sideburns and wearing a military-style uniform.
Witnesses described chaos at the Navy Yard after shots were fired inside the building around 8:20 a.m., sending frantic employees and civilians running for safety, CNN reports.
Authorities haven't established a motive for the shooting and don't suspect it's a result of terrorism.
The Washington Post says Alexis, a military contractor, spent nearly four years in the Navy as a full-time reservist and was discharged in January 2011. ABC News says Alexis was an aviation electrician, but it's unclear why he he was discharged.
The incident represents the single worst loss of life in the District since an airliner plunged into the Potomac River in 1982, killing 78, the Washington Post said.