WASHINGTON, April 3, 2014 - Army Spc. Ivan A. Lopez, 34, was the gunman in yesterday's shooting at Fort Hood, Texas, the installation commander said today.

Army Lt. Gen. Mark A. Milley said there are "strong indications" that the shootings were an isolated incident that may have been triggered by a verbal altercation Lopez had with another soldier or soldiers. What triggered the event remains under investigation, he said.

"At this point, we have not ruled out anything whatsoever, and we are committed to letting the investigation run its course," the general said, "but we have, again, no indications at this time of any links to any terrorist organizations of any type, either national or international."

There are currently no signs that Lopez was targeting specific people, said Milley, who also serves as III Corps commander.

An Army Criminal Investigation Command unit is serving as the lead investigating agency, the general said.

"They are right now synchronizing all of the investigative work -- the federal, state, local and Army agencies throughout Fort Hood and the surrounding area," the general said. "They are interviewing witnesses, and that is an ongoing and active investigation."

Milley asked that the media respect the integrity of the investigation and avoid interviewing potential witnesses.

Three soldiers were killed and 16 were wounded in the shootings before Lopez turned his gun on himself. Nine victims remain hospitalized at Scott and White hospital in Temple, Texas, while three are at Darnall Army Community Hospital at Fort Hood. Four of the soldiers have been released, Milley said.

A memorial service for the fallen is planned for early next week, he said, noting that more details will be released soon.

With about 70,000 people working at Fort Hood and about 40,000 associated family members, it would not be realistic to conduct pat-down searches of everyone entering the installation as some have suggested, the general said.

Lopez, originally from Puerto Rico, arrived at Fort Hood only recently from Fort Bliss, Texas, after reclassifying from infantryman, the general said. At Fort Hood, Lopez was assigned to the 49th Transportation Battalion, 13th Sustainment Command, as a truck driver, he added.

While the Army has "very strong evidence" that Lopez had a medical history that indicates he had an unstable psychiatric or psychological condition, the general said, no specific incidents led to Lopez' transfer to Fort Hood, and he was not transferred to join the Warrior Transition Unit there.

"We do know that he was under treatment, so he was in the system and he was being looked at," Milley said.

There were several instances of clear heroism as yesterday's events unfolded, the general said, specifically citing a female military police officer "who clearly performed her duty exceptionally well." Others inside some of these buildings performed heroic personal acts in saving others, he added. He declined to identify the military police officer, noting that she is germane to the ongoing investigation.

At least one chaplain shielded and saved other soldiers by breaking out windows and helping them to safety, Milley said, and the initial triage work performed by the staff at Darnall Army Medical Center was "exceptional," easily rising to the levels of combat medical standards, he noted.

The first 911 calls came in at 4:16 CDT yesterday, he said. Two wounded soldiers made the call, the general said, noting that he's now had the chance to speak with them both at Scott and White Medical Center.

"The shooting began just a few minutes prior to that," Milley said, adding that military police arrived four minutes after the 911 call. The female MP began working the scene with other law enforcement officers, the general said, and a short time later Lopez approached within 20 feet of her position.

Lopez put his hands up, Milley said, but then went under his jacket and pulled out a .45-caliber Smith & Wesson handgun. Perceiving a threat, the MP engaged Lopez with small-arms fire, and Lopez responded by shooting himself in the head, the general said.