Army Lt. Gen. Mark Milley held a news conference tonight on the shooting at Fort Hood in Texas.

The shooter, who Milley declined to identify at this time, fired shots at about 4 p.m. local time. Within 15 minutes, first responders arrived at the scene. A female officer engaged the shooter in a parking lot, and he died of a self-inflicted gunshot wound, Milley said.

UPDATE, April 3 at 9:00a ET: The gunman has been identified as Spc. Ivan Lopez, an Iraq War veteran being treated for mental illness, authorities say. 

Four people, including the shooter, are dead. Another 16 were injured and are being treated. All of the victims were members of the military.

At this time, there is no indication that this is related to terrorism, though it has not been ruled out. The investigation is ongoing.

Milley is withholding the shooter’s name pending notification of his family. He said that the shooter had behavioral and mental health issues and was being treated. He was undergoing a diagnosis process for PTSD but had not yet been diagnosed. The shooter was on medication.

The shooter served four months in Iraq in 2011, and was not a wounded warrior, Milley said. He had a self-reported traumatic brain injury. The shooter was married and had a family.

Milley said that the shooter was carrying a .45 caliber Smith & Wesson. It was not registered on base.

After shots were fired, a shelter-in-place was put into effect. The lockdown has since been lifted.

Read more about the Fort Hood shooting from Fox News:

WATCH: Hospital Delivers News Conference on Fort Hood Shooting

VIDEO: Obama ‘Heartbroken’ Over Fort Hood Shooting

UPDATES: Official Says 4 Dead, Including Gunman, in Fort Hood Shooting