Aaron Alexis, the man accused of killing 13 people and wounding at least eight at the Washington Navy Yard on Monday, had received treatment for serious mental illness, including "hearing voices," according to a report Tuesday morning from the Associated Press.

The Washington Post has more on Alexis' struggle with mental illness:

"A month before a murderous rampage at the Washington Navy Yard, Aaron Alexis called the police in Rhode Island to complain that he had changed hotels three times because he was being pursued by people keeping him awake by sending vibrations through the walls.

When officers came to his hotel room early on Aug. 7, Mr. Alexis told them that a person he had argued with at an airport in Virginia “has sent three people to follow him” and that they were harassing him with a microwave machine, according to a Newport, R.I., police report. Mr. Alexis said he had heard “voices speaking to him through the wall, flooring and ceiling,” the report said.

“These two incidents combined suggest to me a very flawed system for granting security clearances,” said Senator Susan Collins, Republican of Maine, who called for a Congressional investigation into the granting of security clearances to government contractors. “Who knows how many other Snowdens and Aaron Alexises are out there?”

Mr. Alexis told the police he was a Navy contractor, and then twice that month he sought treatment from the Veterans Affairs Department for psychiatric issues, according to a senior law enforcement official. But it did not raise a red flag that might have prevented him from entering the military base in Washington where, the authorities say, he killed 12 people on Monday."

With each new revelation of infractions while still a Navy reservist, mental health problems, and run-ins with the police over gun violence, the list of questions as to how Alexis was able to gain and keep a security clearance from the Defense Department that gave him access to military bases, including the navy yard, where he was shot to death by the police.

Yet in each instance, Alexis’s behavior managed to fall just below a level that would have brought a serious response, such as a less-than-honorable discharge from the military or involuntary commitment to a mental institution, experts and officials said.

The number episodes involving Alexis alone raises questions about the government’s system for vetting people for security clearances, including the thousands of contractors who help run the nation’s military and security system work. And while the cases are very different, the questions are similar to those raised raised about another outside government contractor, Edward J. Snowden, who leaked national intelligence secrets.

Alexis, was in the Navy Reserves and was a practicing Buddhist who once lived in a temple outside Ft. Worth. Alexis was discharged from the Reserves in January 2011 for a “pattern of misconduct,” a Navy official told The Washington Post, although another official said Alexis was given a “general discharge.” Alexis, 34, worked for Hewlett-Packard as a subcontractor and had been scheduled to start work at the Navy yard later this month. Though friends describe him as “such a nice guy,” Alexis had a dangerous police record: he had been arrested twice, once in 2004 for shooting at the tires of a neighbor’s car and again in 2010 for firing a bullet into his Ft. Worth apartment.

WJLA:

"Alexis carried three weapons: an AR-15 assault rifle, a shotgun, and a handgun that he took from a police officer at the scene, according to two federal law enforcement officials who spoke on condition of anonymity because they were not authorized to discuss the investigation. The AR-15 is the same type of rifle used in last year's mass shooting at a Newtown, Conn., elementary school that killed 20 students and six women. The weapon was also used in the shooting at a Colorado movie theater that killed 12 and wounded 70.

Alexis was a full-time Navy reservist, based in Texas, when he left service in 2011.

Alexis had been working for the fleet logistics support squadron No. 46, in Fort Worth, Texas. The Navy says his home of record was New York City.

The military reports Alexis enlisted on May 5, 2007 and received the National Defense Service Medal and the Global War on Terrorism Service Medal – one for servicing during a time of national emergency, and another for serving post-9/11."

Embry-Riddle Aeronautical University says that Alexis was an online student pursuing a bachelor's degree in aeronautics. He began classes in July 2012.

During a Monday night press conference, it was confirmed that the description of another possible shooter has been lifted, ruling out the suspect dressed in olive drab. MPD is continuing to pursue the possibility of a second suspect, though the department is "comfortable that we have the one person responsible for loss of life today."

There is presently no known motive for the deadly shootings.

President Obama on Tuesday ordered the White House budget office to conduct a government-wide review of policies for security clearances for contractors and employees in federal agencies.

He also called, again, for Congress to enact legislation to keep guns out of the hands of criminals and those with mental illness.

“I do get concerned that this becomes a ritual that we go through every three, four months, where we have these horrific mass shootings,” he said.