Four people are dead and 16 were injured after a soldier opened fire at Fort Hood.

Fort Hood, a military post in Kileen, Texas, is the same site where 13 were killed in 2009 in a shooting.

The suspected shooter is Spc. Ivan Lopez. Lopez, 34, who is suspected to have killed himself when confronted by a police officer. He had mental issues and was being treated for depression and anxiety.

"We do know that this soldier had behavioral health and mental health issues and was being treated for that," said Lt. Gen. Mark Milley, head of the Army's III Corps at the Texas post.

Officials don't know what could have caused Lopez to turn on his fellow soldiers, but they do know he was being evaluated for post traumatic stress disorder.

Lopez served four months in Iraq in 2011, but did not see combat. He diagnosed himself with a traumatic brain injury.

Army John McHugh said Lopez was examined by a psychiatrist just last month. He displayed no violent or suicidal tendencies and the only condition that was found was difficulty sleeping. For this, he was prescribed Ambien.

Lopez originally joined the Army as an infantryman in 2008, but switched to truck driver, the same position he had in Iraq.

Authorities are scheduled to speak to Lopez's wife and search his home and computer to see if they can determine a motive for the attack.

With Wednesday's attack, the debate continues on the policy of soldiers having personal weapons on bases. Currently, they are not allowed to have personal or concealed weapons.

"We need to harden our military bases so this can't happen, and one possible way to do that is to allow our veterans and active duty military ... to carry weapons," said Rep. Michael McCaul, R-Texas, chairman of the House Homeland Security Committee. 

Besides that policy, base security nationwide is being questioned. After the 2009 attack and the 2013 Navy Yard shooting, security has been examined closely.

"Obviously when we have these kinds of tragedies on our bases, something's not working." Defense Secretary Chuck Hagel said.