According to sources, Hasan, who is either 39 or 40, attended the Uniformed Services University of the Health Sciences in Bethesda, MD. He graduated in 2003 with a degree in Osteopathy and later finished his residency as a psychiatrist.
In 2009, Hasan completed a fellowship in Disaster and Preventive Psychiatry at the Center for Traumatic Stress.
He was promoted to major status in May, according to the Army Times.
According to the Associated Press, Retired Army Col. Terry Lee told Fox News that Hasan had expressed hope that President Obama would pull troops out of Afghanistan and Iraq and often argued with others who supported the wars.
Fort Hood, located just 60 miles north from Austin, is the largest U.S. military installation in the world, and has suffered the greatest number of casualities of all American bases in the war on Iraq.
The base is a 340 sq. mile facility located in Killeen, Texas and is home to the 1st Cavalry Division, which was one of the first groups of soldiers deployed to Iraq.
Cone said that a gunman entered a facility known as the Soldier Readiness Facility, where soldiers who are preparing to deploy go for last minute medical check ups and dental treatment. Sources told ABC News that the soldiers gathered there were getting ready to deploy to Iraq.
Thursday is a day that brings many different military units to the facility to make up miss appointments, said Cone, which explains why the victims were part of different branches.
"This could have been much worse, as horrible as this was, it could have been much worse," said Cone.
Cone praised the soldiers' quick response and knowledge of first aid techniques in saving so many lives.
The gunman used two handguns, Cone said. He wasn't sure if the shooter reloaded the weapons during the attack.
Cone said he did not believe the guns used were military weapons.
"As a matter of practice, we don't carry weapons here, this is our home," said Cone.
Schools on the base were also placed on lockdown. A message on Fort Hood's public affairs office Web site read, "Organizations/units are instructed to execute a 100 percent accountability of all personnel. This is not a Drill. It is an Emergency Situation."
According to a source on the base, it is rare for firearms to be on the base because they are locked up.
Homeland Security said it is still gathering information and that the "Army is taking the lead" as of now. FBI agents from Waco and Austin, Texas, are being deployed to the scene.
An army spokesman said that unit commanders have been instructed to account for all of their personnel.
"The immediate concern is to make sure that all of our soldiers and family members are safe and that's what commanders have been instructed to do," said Jay Adams of First Army, Division West, located at Fort Hood.
Cone emphasized the post's plans to amp up security in the coming days.
The CounterTerrorist Unit said they have "no word" yet on whether this incident was terrorism-related.
At least six victims are being treated at the Metroplex Hospital five miles away. Area hospitals are all requesting blood donations to treat victims.
Nasser Atta contributed to the reporting of this story from Ramallah.