Investigators seek motive in deadly DC Navy Yard shooting

Investigators on Tuesday questioned how former U.S. Navy reservist Aaron Alexis -- who had a string of run-ins with the law -- was able to get clearance to enter the Washington Navy Yard, where, police say, he killed 12 people Monday. Alexis died during the shooting spree, leaving his motive in the rampage a mystery.

The FBI said it believes that Alexis entered Building 197 at the facility -- with a valid pass -- carrying a shotgun he legally bought and that he obtained a handgun once inside.

It is believed that the alleged shooter was able to buy the firearm from a registered gun shop despite having had known mental-health issues. Police in Newport, R.I., say they contacted Naval Police just last month after Alexis wanted to file a harassment report, claiming that three people were following him, talking to him through his hotel walls and "sending vibrations into his body," according to a police report.

Alexis arrived in Washington on Aug. 25, the FBI said, and had been staying at local hotels. Just one day before the Navy Yard shooting, the suspect visited a gun range in Virginia, hinting that his alleged actions may have been premeditated.

He received an early -- but honorable -- discharge from the Navy Reserve in 2011, a Navy official said Tuesday. Before issuing the discharge, however, the Navy had pursued a general discharge against Alexis after eight to 10 misconduct charges ranging from traffic offenses to disorderly conduct, according to Navy officials.

U.S. law-enforcement officials told The Associated Press Tuesday that he had serious mental issues and that he suffered from paranoia and a sleep disorder and was prone to flashes of rage.

Family members told investigators Monday that Alexis had been treated for mental-health issues since August by the Department of Veterans Affairs, officials said.

The Navy did not declare Alexis mentally unfit, which would have rescinded a security clearance that he had from his time in the Navy Reserve. Officials said Alexis was working on a Defense project for a subcontractor for computer giant Hewlett-Packard.

But officials described Alexis' four-year stint in the Navy, from 2007 to 2011, as troubled.

He was arrested on Sept. 4, 2010, in Fort Worth, Texas, on a misdemeanor charge of discharging a firearm. The case was dropped when investigators determined he was cleaning his gun before it accidentally fired, Tarrant County prosecutors said.

He was also arrested in Seattle in 2004 for shooting a construction worker's car tires in what Alexis described as an anger-fueled "blackout," according to the Seattle Police Department.

But his motive for the Navy Yard shooting remains a mystery. Officials stressed that they have uncovered no connections between Alexis and international or domestic terrorism, and investigators have found no manifesto or other writings suggesting a political or religious motivation.

The FBI, meanwhile, appealed to the public for information on the 34-year-old from Fort Worth.

"No piece of information is too small," said Valerie Parlave, assistant director of the FBI's Washington field office. "We are looking to learn everything we can about his recent movements, his contacts and his associates."

Monday's attack was the deadliest on a military installation in the U.S. since the 2009 Fort Hood, Texas, massacre that left 13 dead and wounded 30.

The Washington violence has prompted the Defense Department to announce Tuesday that it will review security for and access to all its installations worldwide. Also Tuesday, data from a still unreleased yearlong audit of the Navy security system surfaced that indicated 52 felons have had routine unauthorized access to Navy facilities.

At the time of Monday's shooting, Alexis was an employee with The Experts, a company that was a Defense Department subcontractor on a Navy-Marine Corps computer project, officials said.

Washington Mayor Vincent Gray said he was baffled that Alexis got the job he had.

"It's hard to believe that someone with a record as checkered as this man could get clearance, credentials, to get on the base," Gray told CNN. "I just met with the commandant of the Washington Naval Yard last week. We know this is one of the most secure facilities in the nation. So how this could happen is beyond belief."

Outside the National Archives, where the U.S. Constitution is stored, visitors seemed resigned to senseless acts of violence.

“Not a whole lot can be done," Kaleb Steemeyer, 30, a writer and bartender from Orlando, Fla., told Al Jazeera America. "He was a legal citizen with legal weapons. I don't think taking weapons out of the hands of law-abiding citizens (is the answer), because criminals don't get weapons through those venues."

"I think if someone wants to get in anywhere and kill someone, they're going to do it," said Lori Tolliver, 30, of Statesville, N.C. "If you have it in your mind to do it, you're going to do it."

Authorities said Alexis appears to have acted alone in the attack at the sprawling military complex, where he injured 14 others.

"We do now feel comfortable that we have the single and sole person responsible for the loss of life inside of the base today," Washington Police Chief Cathy Lanier told reporters late Monday.

The first shots rang out at 8:15 a.m. Monday in Building 197 at the headquarters of the Navy's Sea Systems Command. At one point, Alexis was perched high in an atrium picking off victims in a cafeteria below, investigators said. That's where most of the victims were found.

The roughly 3,000 people who work at the Navy Yard were told to stay in place as officers and tactical teams started hunting for the shooter.

"We were hunkered down because we had heard previous gunshots," said Navy Capt. Mark Vandroff. "We were on the floor, and then we heard gunfire, and there were two bullet holes in the top of the wall of the conference room."

The shooting left Washington on edge, and there was a security scare at the White House later Monday when a man apparently threw firecrackers over a fence at the president's residence; he was swiftly arrested.

President Obama ordered flags flown at half-mast in the capital until Friday as a mark of respect for the dead. He called the shooting a "cowardly act" and said that the U.S. was confronting "yet another mass shooting," saying troops in the military should not have to face danger at home.

Al Jazeera and wire services. With reporting from Wilson Dizard from Washington.