An Iraq War veteran being treated for mental illness opened fire at Fort Hood, Texas, on Wednesday afternoon, leaving four people dead, including the gunman, and 16 people wounded.

The soldier, identified as 34-year-old soldier Ivan Lopez, turned the gun on himself and died of a self-inflicted wound after opening fire at the military base where more than a dozen people were slain in an attack in 2009, according to authorities.

Lopez was identified by U.S. Rep. Michael McCaul, chairman of the House Homeland Security Committee.

“We do not know a motive,” Lt. Gen. Mark A. Milley told reporters at a press conference Wednesday night.

“But we know this soldier to have behavioral health and mental health issues,” Milley said.

Milley also said authorities did not believe the attack was related to terrorism, but that they are not ruling anything out at this time.

Lopez, who was being treated for depression and anxiety, went into two buildings on the base and opened fire before he was confronted by military police, Milley said.

The shooting occurred at approximately 4 p.m. on Wednesday. Emergency personnel, the FBI and SWAT teams were called in to the base following the shooting.

The shooter used a .45 caliber Smith & Wesson semi-automatic pistol that had been purchased recently, Milley added.

Nine of the victims in the shooting were hospitalized with gunshot wounds at Scott & White hospital in Temple, Texas. As of early Thursday morning, three victims were listed as being in critical condition.

According to Milley, all of the shooting victims were members of the military.

Lopez served for four months in Iraq in 2011, and was undergoing an evaluation for post traumatic stress disorder, according to Milley. Lopez arrived in Fort Hood, one of the largest U.S. Army bases, in February from another military base.

In 2009, 13 people were killed and more than 30 wounded in a mass shooting at Fort Hood by then-Maj. Nidal Hasan, an army psychiatrist. A U.S. Senate report following the incident described it as the worst attack on American soil since the terrorist attacks of Sept. 11, 2001, The FBI said that though Hasan expressed anti-American sentiments prior to the shooting, he had had no ties to terrorist groups.

Hassan was sentenced to death after admitting to the shooting during his court martial hearing in August 2013, and is now on death row.

“We’re following it closely. The situation is fluid right now,” President Obama told reporters in Chicago.  He said that investigators would “get to the bottom of exactly what happened.”

“We’re heartbroken something like this might have happened again,” the president said.

Image via Wikimedia Commons