Washington Navy Yard gunman Aaron Alexis 'was hearing voices in his head' In a news conference a day after a mass shooting at the U.S. Naval Yard, FBI agent Valerie Parlave told reporters shooting suspect Aaron Alexis, armed with a shotgun, used a valid pass to enter Building 197. AARON Alexis is a contradiction: an ex-US Navy reservist, a Defence Department contractor, a Buddhist convert but also a man with anger management issues. A profile has begun to emerge of the man authorities identified as the gunman in a mass shooting at a Navy complex in Washington, DC, that left 13 people dead, including him. A shooting rampage at a US Navy complex in Washington DC has left 13 people dead, including a gunman. FBI photo of Aaron Alexis, the man identified as the US Navy Yard shooter. A joint press conference held at 2pm (4am AEST) failed to reveal many more details with the FBI refusing to go into what Alexis's motive might have been. DC Police Chief Cathy Lanier said hundreds of tips had been received from the public and urged anyone who might know more about the shooting or about Alexis to call the FBI. "There is no piece of information too small," she said. While some neighbours and acquaintances described the 34-year-old Alexis as "nice," his father once told detectives in Seattle that his son had anger management problems related to post-traumatic stress brought on by the terrorist attacks of September 11, 2001. Alexis also complained about the Navy and being a victim of discrimination. US law enforcement officials said that Alexis had been suffering from a number of serious mental issues, including paranoia and a sleep disorder. He also had been hearing voices in his head, the officials said. Alexis had been treated since August by the federal Veterans Administration for his mental problems, the officials said. They spoke on condition of anonymity because the criminal investigation was continuing. The Navy had not declared him mentally unfit, which would have rescinded a security clearance Alexis had from his earlier time in the Navy Reserves. Family members told investigators Alexis was being treated for his mental issues. At the time of the shootings, he worked for The Experts, a subcontractor on an HP Enterprise Services contract to refresh equipment used on the Navy Marine Corps Intranet network. Alexis lived in Seattle in 2004 and 2005, according to public documents. In 2004, Seattle police said Alexis was arrested for shooting out the tyres of another man's vehicle in what he later described to detectives as an anger-fuelled "blackout." According to an account on the department's website, two construction workers had parked their car in the driveway of their worksite, next to a home where Alexis was staying. The workers reported seeing a man, later identified by police as Alexis, walk out of the home and fire three shots into the rear tyres. Workers at the construction site told police Alexis had stared at them daily for several weeks. The owner of the construction business told police he believed Alexis was angry over the parking situation. Police eventually arrested Alexis, found a gun and ammunition in his room and booked him into jail for malicious mischief. According to the police account, Alexis told detectives he perceived he had been "mocked" by construction workers the morning of the incident. Alexis also claimed he had an anger-fuelled "blackout," and could not remember firing his gun until an hour after the incident. Alexis also told police he was present during "the tragic events of September 11, 2001" and described "how those events had disturbed him." In 2007, he enlisted in the Navy reserves, serving through 2011, according to Navy spokeswoman Lt. Megan Shutka. While he was still in the reserves, a neighbour in Texas reported she had been nearly struck by a bullet shot from his downstairs apartment. Alexis admitted to firing his weapon but said he was cleaning his gun when it accidentally discharged. This undated cell phone photo provided by Kristi Kinard Suthamtewakul shows a smiling Aaron Alexis in Fort Worth, Texas. After leaving the reserves, Alexis worked as a waiter and delivery driver at the Happy Bowl Thai restaurant in a suburb of Fort Worth, Texas, according to Afton Bradley, a former co-worker. Alexis left in May, Mr Bradley said. Having traveled to Thailand, Alexis learned some Thai and could speak to Thai customers in their native language. "He was a very nice person," Mr Bradley said in a phone interview. It kind of blows my mind away. I wouldn't think anything bad at all. In the early 2000s, before he moved to Seattle, Alexis lived with his mother in an apartment in New York City, said Gene Demby, who said he dated one of Alexis' younger sisters at the time. "I wouldn't call him nice, but he seemed harmless, if really awkward," said Mr Demby. He was insecure. He was like a barbershop conspiracy theorist, the kind of guy who believes he's smarter than everyone else. He also was kind of like perpetually aggrieved, but not megalomaniacal or delusional. Restaurant owner Oui Suthamtewakul, right, and Micheal Ritrovato speak about working with Aaron Alexis , who was once employed by Suthamtewakul. AP Photo/LM Otero Embry-Riddle Aeronautical University, which offers online courses in aviation and aerospace, confirmed that Alexis was enrolled as an online student, started classes in July 2012 and was pursuing a bachelor's of science in aeronautics. "We are cooperating fully with investigating officials," the university said. All 12 of his victims have now been identified and include Michael Arnold, 59; Sylvia Frasier, 53; Kathy Gaarde, 62; John Roger Johnson, 73; Frank Kohler, 50; Kenneth Bernard Proctor, 46; Vishnu Pandit, 61; Arthur Daniels, 51; Mary Francis Knight, 51; Gerald Read, 58; Martin Bodrog, 54; Richard Michael Ridgell, 52. Two DC Metro Police officers put their gear uonas they respond to a reported shooting at an entrance to the Washington Navy Yard.