ABC News is identifying that gunman as Specialist Ivan Lopez.
The shooting happened around 4pm Wednesday and last about 15 minutes. Authorities say the gunman, a married soldier who served four months in Iraq in 2011, began shooting at one location, then got into a car and opened fire at second before he was engaged by a female soldier. At that point, he pulled out a gun and fatally shot himself in the head.
Fort Hood officials said all the victims were military service members and those who were injured were transported to Carl R. Darnall Medical Center and other local hospitals. Scott & White Memorial Hospital, another hospital in the Killeen area, said it has received nine patients with injuries to the chest, neck and extremities.
Officials said the gunman used a semi-automatic .45-caliber handgun that he had recently purchased but not registered on base, as required. ATF is conducting an urgent trace of the gun, which is standard protocol in these types of incidents.
Authorities did not specify a motive but said they don't expect this to be related to any terrorism. They said the gunman is married and has children; he was taking medication and seeking help for depression and anxiety and was undergoing a diagnosis process for PTSD but hadn't yet been diagnosed.
The military base was under lockdown for about four and half hours Wednesday.
Many people and even Fort Hood officials took to social media to warn others about the active shooting. On its Twitter feed and Facebook page, Fort Hood ordered everyone on base during the shooting to "shelter in place." The 1st Cavalry Division, which is based at Fort Hood, sent a Twitter alert telling people on base to close doors and stay away from windows.
The FBI, ATF, Texas Rangers, among others, are helping in the investigation. Meanwhile, the Red Cross also is accepting monetary donations online at www.redcross.org.
Family notifications are ongoing; the names of the deceased will not be released until 24 hours after the next of kin have been notified. Family members can call the Family Assistance Center Hotline at 254-288-7570 or 866-836-2751.
Chaplains have setup family counseling centers on and off post. Locations are the Spirit of Fort Hood Chapel and Scott & White Hospital.
Outside the base, some relatives of soldiers waited for news about their loved ones.
Tayra DeHart, 33, said she had last heard from her husband, a soldier at the post, that he was safe, but that was hours earlier.
"The last two hours have been the most nerve-wracking I've ever felt. I know God is here protecting me and all the soldiers, but I have my phone in my hand just hoping it will ring and it will be my husband," DeHart said.
Brooke Conover, whose husband was on base at the time of the shooting, said she found out about it while checking Facebook. She said she called her husband, Staff Sgt. Sean Conover, immediately to make sure he was OK, but he couldn't even tell her exactly what was going on, only that the base was locked down.
"I'm still hearing conflicting stories about what happened and where the shooting was exactly," Conover said, explaining that she still doesn't know how close the incident was to her husband.
"I just want him to come home," said Conover, who moved to Fort Hood with her husband and three daughters two years ago.
In Chicago, President Barrack Obama vowed that investigators will get to the bottom of the shooting, seeking to reassure the nation whose sense of security once again has been shaken by mass violence
In a hastily arranged statement, Obama said he and his team were following the situation closely but that details about what happened at the sprawling Army post were still fluid. He said the shooting brought back painful memories of the 2009 attack.
Obama reflected on the sacrifices that troops stationed at Fort Hood have made - including during multiple tours to Iraq and Afghanistan.
"They serve with valor, they serve with distinction and when they're at their home base, they need to feel safe," Obama said. "We don't yet know what happened tonight, but obviously that sense of safety has been broken once again."
The president spoke without notes or prepared remarks in the same room of a steakhouse where he had just met with about 25 donors at a previously scheduled fundraiser for the Democratic National Committee. White House officials quickly pushed tables to the side of the room to make room for Obama to speak to the nation.
The base was the scene of a mass shooting in 2009. Thirteen people were killed and more than 30 wounded in what was the deadliest attack on a domestic military installation in history.
Army psychiatrist Nidal Hasan was convicted and sentenced to death last year in the Nov. 5, 2009, attack on his fellow soldiers as they waited inside a crowded building at Fort Hood. Soldiers there were waiting to get vaccines and routine paperwork after recently returning from deployments or while preparing to go to Afghanistan and Iraq.
According to testimony during Hasan's trial last August, Hasan walked inside carrying two weapons and several loaded magazines, shouted "Allahu Akbar!" - Arabic for "God is great!" - and opened fire with a handgun.
Witnesses said he targeted soldiers as he walked through the building, leaving pools of blood, spent casings and dying soldiers on the floor. Photos of the scene were shown to the 13 officers on the military jury.
The rampage ended when Hasan was shot in the back by Fort Hood police officers outside the building, which left him paralyzed from the waist down. Hasan is now on death row at the military prison at Fort Leavenworth in Kansas.
Stay with ABC13 Eyewitness News for the latest on this developing story on air, online and on our news apps. The Associated Press contributed to this report
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