A U.S. naval reservist launched an attack Monday morning inside a building at a U.S. Navy complex in the heart of Washington on Monday, killing 12 people before he lost his life as well.
Meanwhile, the White House was locked down after a security alert over reported gunshots.
Police identified the alleged shooter as 34-year-old Aaron Alexis, of Forth Worth, Texas, who served full-time in the Navy from 2007 to 2011, the FBI and Pentagon said.
Alexis was at some point a civilian contractor for the U.S. Navy in the information technology area, Navy Secretary Ray Mabus said, according to Reuters.
His ties to the Navy could help determine his motive and how he had access to the Navy Yard.
“At one point, he was a Navy contractor. Whether he was today, I don’t know,” Mabus told CNN.
Authorities said they were looking for a second possible attacker who may have been disguised in a military-style uniform.
The shooting sparked a massive show of force as police and federal agents surrounded the Navy Yard, cordoning off streets only blocks from the U.S. Capitol, home of Congress.
Officials gave no indication of any link to terrorism but said the motive for the attack on the installation was unknown.
The U.S. Senate was put on lockdown Monday following shooting.
President Barack Obama said he was mourning “yet another mass shooting” and called it a “cowardly act,” Associated Press reported.
He ordered flags be lowered to half-mast through Friday.
“We are confronting yet another mass shooting, and today it happened at another military installation, in our nation’s capital,” said Obama, who vowed to enact “sensible” gun control measures after a gunman shot dead 20 school children and six adults at an elementary school in Connecticut last December.
“They know the dangers of serving abroad, but today they face the unimaginable violence that they wouldn’t have expected here at home,” Obama said.
Despite a string of shootings during his presidency, Obama has been powerless to get gun control legislation passed amid a fierce backlash from conservative politicians and the gun industry lobby.