Washington, Sep (IANS): Investigators were Tuesday searching for clues as to what led a lone gunman to kill 12 people, including an Indian-American, at a US naval base in an audacious mass shooting in the heart of the US capital before being shot dead.

No official details were available about Vishnu Pandit, 61, who was among seven of the 12 shooting victims identified by authorities Monday night. But a brief Washington Post profile suggested he lived in North Potomac, a Washington suburb in neighbouring Maryland.

One neighbour, Zhaohua Zhou, told the post that a steady stream of cars arrived late Monday outside Pandit's home.

"I'm astonished," Zhou said. "I'm just so sorry."

Another neighbour, Mike Honig, told the paper that Pandit and his wife have lived in the neighbourhood for at least 20 years. He described Pandit as "a very nice man with an Irish setter".

"All of the neighbours are doing all they can," Honig was quoted as saying. "It's a terrible tragedy... It's a stain and strain on the nation that we haven't put public safety laws in place to prevent this sort of tragedy."

A man who answered the phone at the Pandit house said the family did not want to comment, the Post said.

Meanwhile, the Federal Bureau of Investigation (FBI) identified the alleged shooter at the sprawling Washington Navy Yard complex in southeast Washington not too far from the Capitol and the White House as Aaron Alexis, 34, of Fort Worth, Texas.

Alexis, who received a general discharge in 2011 from the Navy Reserve, was arrested but not charged in a gun incident in Seattle back in 2004 but still had a security clearance with a military contractor that would have allowed him access to the Navy Yard, officials said.

Besides the 12 dead, Alexis shot and injured several people at the Navy Yard, the Navy's oldest land establishment created in 1799, where several major commands and Navy offices are located and about 16,000 military and civilian personnel work, the Post said.

"There's no question [Alexis] would have kept shooting," Washington police chief Cathy L. Lanier was quoted as saying.

The worst shooting incident at a military installation since 13 people were killed at Fort Hood, Texas, in 2009 began unfolding at 8.20 a.m. when many shots were fired inside the facility.

Air traffic to Reagan National Airport was briefly suspended after the shooting and 10 public and charter schools and a public school administration building in the capital were also placed on lockdown as a precaution.

Officials postponed a Washington Nationals baseball game that was scheduled for Monday night at Nationals Park, just a few blocks away from the Navy Yard.