Aaron Alexis, 34, named as the heavily armed gunman who opened fire at the Washington Navy Yard in Washington D.C.

The Washington Navy Yard gunman who killed 12 today has previously claimed to be suffering from PTSD after helping rescue efforts in New York following the 9/11 terror attacks. Gunman Aaron Alexis was shot dead by responding officers after he opened fire inside a Navy facility around 8:00 a.m. on Monday morning.  It emerged today that he used three guns during the massacre, one of them an AR-15 semi-automatic rifle - the same weapon used in the Sandy Hook and Aurora mass shootings. Since he was identified as the shooter, reports have revealed that it was not the first time he was involved in a shooting.  In 2004, Alexis was arrested in Seattle for shooting the tires of a construction worker's car during what he later called an anger-fueled 'blackout.' 'He said that he didn’t remember pulling the trigger of his firearm until about one hour later,' according to the Seattle police report. Later he said that he felt the intended victim 'disrespected' him. The report states that his father said his anger issues stemmed back to his time in New York where he helped the rescue efforts following the September 11 terrorist attacks.The shooter's father told police 'that his son had experienced anger management problems that the family believed associated [sic] with PTSD.' He was arrested in relation to that incident but never charged, an outcome repeated in Fort Worth, Texas where Alexis was living in 2010.

Then, he was arrested for discharging a firearm when his neighbor reported that he fired a shot into her apartment. At the time, Alexis claimed that his hand slipped when he was cleaning his gun while cooking at the same time, and that he accidentally fired the weapon. New reports also claim that Alexis was arrested for a second time in DeKalb county, Georgia and spent two nights in jail over a disorderly conduct charge but no further details have been released about that incident. 

It emerged today that Alexis used three weapons in yesterday's shooting: a shotgun he is believed to have brought to Navy Yard with him, and two more weapons that officers believe he picked up during the course of the massacre: an AR-15 semi-automatic assault rifle and a handgun.

One report said he took one of the weapons from a police officer as the slayings continued, while the shotgun was reportedly bought at a Virginia gunstore recently.

Last night Staff Sgt. Alonzo Lunsford, who was shot by Nidal Hasan during the 2009 Fort Hood shooting, told CNN's Piers Morgan that 'almost every mass shooting involves an AR-15 assault rifle'.

He added: It's the preferred mass shooter's weapon of choice, but I don't see a logical reason why any civilian needs to have one of these killing machines.'

No motive has been revealed for Monday's shooting, but speculation is growing his dismissal from the U.S. Navy for 'misconduct' in January 2011 may have inspired him to commit deadly revenge.

The Pentagon confirmed that he was awarded the Global War on Terrorism Service Medal and the National Defense Service Medal prior to his discharge in January 2011. 

Family members of the Washington shooter are 'distraught' to learn that he carried out the massacre, relatives told MailOnline today.

Despite the lack of an acknowledged motive, one U.S. official has been quoted as saying Alexis was discharged from the Navy in 2011 following a series of incidents of 'misconduct.'

Law enforcement said that his identity was confirmed by fingerprints and that he served in the U.S. Navy between May 5, 2007 and January 31, 2011.

A U.S. Navy spokesman said Alexis was an 'aviation electrician's mate' – ranked as a third class petty officer – and served at the Naval Air Station in Fort Worth, Texas.

He is reported to have enlisted in New York. The Brooklyn native graduated from boot camp at Great Lakes, Illinois as an airman recruit. Throughout the late 1990s until 2002, he was listed as living in Manhattan and Queens in New York City. He is still registered as a voter in New York City.
Alexis, who worked as a civilian I.T. contractor at the military base in the nation's capital, entered the cafeteria of Building 197 just before 8:15 a.m. brandishing an AR-15 semi-automatic rifle, a shotgun and a handgun, and began shooting.

It is thought that he used an identification card belonging to another employee of the base to gain entry to the heavily secured building where he carried out his deadly attack.

The FBI said that after SWAT teams swarmed the headquarters of the Naval Sea Systems Command, an officer shot Alexis dead.

Witnesses said that during his rampage he appeared to fire at selected targets and not randomly.

The FBI's Washington Field Office also said that it had 'all [it] assets out' in the field as they searched for one other possible shooter described as a black man in his 40s or his 50s.

According to a deleted Linked In profile, Alexis attended Embry-Riddle Aeronautical University and worked for a tech firm.

A former roommate from Ft. Worth, the owner of Happy Bowl Thai restaurant, told NBC News he had not seen the man in three months. Police records reveal that Alexis was arrested for accidentally discharging a firearm at his Ft. Worth home in September 2010. 

A witness who lived in a neighboring apartment told police that she heard a pop and then to her horror a hole appeared in her floor and ceiling.

Alexis told police he was cleaning his gun when while cooking and that his hands were slippery.

All charges against him were dropped.

Speaking after yesterday's slayings, Washington D.C. Metropolitan Police Department chief Cathy Lanier said officers had ruled out the possibility that anyone else was involved in the shootings.

And she said that Alexis had used a valid security pass to get into the Navy Yard building.

Police are investigating whether the ID of a former Navy petty officer called Rollie Chance was used by Alexis to gain entrance to the the Navy Yard compound.

FBI investigators visited Chance's home Monday but have not revealed how Alexis obtained the identification.

'It appears that we have at least 13 fatalities … it doesn’t get much more serious than that, obviously,' added Washington, D.C. Mayor Vincent Gray during an afternoon press briefing.

'We have no known motive at this stage. We will continue the investigation to try and figure out what that motive is.' 

'We don’t have any reason to suspect terrorism, but certainly it has not been ruled out.’

Previously, Lanier said law enforcement was searching for two individuals, one white and one black, but they identified the white individual and cleared him of suspicion.

Witnesses reported one man described as an African-American male dressed in military fatigues and armed with an AR-15 semi-automatic rifle opening fire upon entering the base at the Naval Sea System Command HQ.

Todd Brundidge, an executive assistant with Navy Sea Systems Command, said he and other co-workers encountered a gunman in a long hallway of their building on the third floor. The gunman was wearing all blue, he said.