Story highlights 16 other people were injured at the Army installation 
 
 The suspect died from a self-inflicted gunshot wound 
 
 The soldier had mental health issues, an official says 
 
 Incident may have started as a soldier-on-soldier attack, sources say 
 
 Authorities have identified the man who opened fire at Fort Hood in Texas on Wednesday, killing three people before committing suicide, as Specialist Ivan Lopez. 
 
 Sixteen more people were injured Wednesday when he opened fire at Fort Hood, the sprawling Army post in Texas still on edge after a mass shooting there left 13 dead in 2009, officials said. 
 
 The gunman also died. He was engaged by military police before he fatally shot himself in the head, said the Army post's commander, Lt. Gen. Mark A. Milley. 
 
 The suspect, a soldier who had served in Iraq, "had behavioral health and mental health" issues, Milley told reporters late Wednesday. 
 
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 The general said there was no known motive for the shooting. 
 
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 "There is no indication that this incident is related to terrorism, although we are not ruling anything out," he said. 
 
 The initial report is the incident started as a soldier-on-soldier attack, law enforcement sources told CNN. 
 
 Scott & White Hospital in Temple, Texas, was treating eight patients with another expected to arrive shortly, said Dr. Glen Couchman, the chief medical officer. Three patients were in critical condition, while "the remaining are all seriously injured," he said. 
 
 Other patients were taken to Darnall Army Medical Center, not far from the Medical Brigade building where the shooting occurred, according a soldier who lives nearby and spoke on the condition of anonymity. 
 
 The suspected shooter was wearing combat fatigues, said a U.S. official briefed on the shooting. He was armed with a .45-caliber Smith & Wesson handgun that he purchased recently, said Milley. 
 
 President Barack Obama was briefed and said Wednesday evening "we're heartbroken something like this might have happened again." 
 
 He was referring to the November 2009 massacre. 
 
 "I want to just assure all of us we are going to get to the bottom of exactly what happened," the President said. 
 
 While aboard Air Force One, Obama received an update from top defense and FBI leaders about Wednesday's shooting at Fort Hood, the White House said in a statement. 
 
 He commended "military personnel, first responders, and medical staff who responded swiftly and heroically to the horrific shooting." 
 
 The President also called for "his team to utilize every resource available to fully investigate the shooting." 
 
 Defense Secretary Chuck Hagel also was monitoring the situation. He described what happened as a "terrible tragedy." 
 
 Earlier, Fort Hood's official Twitter feed asked that all personnel on post shelter in place. 
 
 11 photos: Fort Hood shooting 11 photos: Fort Hood shooting Fort Hood shooting – Luci Hamlin and her husband, Spc. Timothy Hamlin, wait to get back to their home at Fort Hood after a shooting at the Texas Army post on Wednesday, April 2. Multiple people were killed and others injured when a shooter opened fire, a senior military official and law enforcement official told CNN. The officials said the suspected shooter was among the dead. Hide Caption 1 of 11 11 photos: Fort Hood shooting Fort Hood shooting – A police officer checks drivers' IDs outside the main gate at Fort Hood. Hide Caption 2 of 11 11 photos: Fort Hood shooting Fort Hood shooting – Krystina Cassidy and Dianna Simpson, waiting outside the Bernie Beck Gate at Fort Hood, try to contact their husbands, who are stationed at the post. Hide Caption 3 of 11 11 photos: Fort Hood shooting Fort Hood shooting – A Bell County Sheriff's Department official stands near a vehicle as cars are checked at the Bernie Beck Gate. Hide Caption 4 of 11 11 photos: Fort Hood shooting Fort Hood shooting – An ambulance makes its way to Fort Hood. Hide Caption 5 of 11 11 photos: Fort Hood shooting Fort Hood shooting – Military personnel and civilians wait outside Fort Hood for updates on the situation. Hide Caption 6 of 11 11 photos: Fort Hood shooting Fort Hood shooting – Vehicles wait at a closed entrance to Fort Hood. Hide Caption 7 of 11 11 photos: Fort Hood shooting Fort Hood shooting – A military police officer stops a car. Hide Caption 8 of 11 11 photos: Fort Hood shooting Fort Hood shooting – Traffic near the main gate of Fort Hood. Hide Caption 9 of 11 11 photos: Fort Hood shooting Fort Hood shooting – Lt. Savanah Hess, a nurse, waits in her car to enter the locked-down post. Hide Caption 10 of 11 11 photos: Fort Hood shooting Fort Hood shooting – Military police direct traffic outside Fort Hood. Hide Caption 11 of 11 
 
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 Sheriff's deputies from Bell County and state troopers assisted by securing the area around the post, according to Bell County Sheriff's Lt. Donnie Adams. Authorities in the town of Killeen, just outside the gates, were also standing by to help. 
 
 "We are very concerned. Fort Hood is always there for us and we want to be there for them," said Killeen Mayor Dan Corbin. 
 
 He continued: "They are used to dealing with combat situations, and I'm sure they are very capable of handling this." 
 
 The lockdown was lifted just prior to 9 p.m. (10 p.m. ET), military personnel at the front gate told CNN. 
 
 On November 5, 2009, Army Maj. Nidal Malik Hasan opened fire at Fort Hood, killing 13 people and injuring 32. 
 
 He shot fellow soldiers at the processing center. Prosecutors maintained that the American-born Muslim underwent a progressive radicalization that led to the massacre. 
 
 Hasan allegedly picked that day because it was when the units he was scheduled to deploy with to Afghanistan were scheduled to go through the processing center. 
 
 The former Army psychiatrist was convicted of premeditated murder, and a military jury recommended that Hasan be put to death. 
 
 Wednesday's shooting reminded many in the central Texas community of that incident. 
 
 "Today, Ft. Hood was once again stricken by tragedy. As Texans, our first priority must be caring for the victims and their families. Ft. Hood has proven its resilience before, and will again. Texas will support those efforts in any way we can, with any resources necessary," said Gov. Rick Perry. 
 
 U.S. Sen. John Cornyn said in a statement that no community should have to experience such violence once, let alone twice. 
 
 "Tonight, Texans' hearts are once again very heavy. The scenes coming from Fort Hood today are sadly too familiar and still too fresh in our memories," he said. 
 
 According to the Fort Hood website, the post is one of the largest in the world with 45,414 assigned soldiers and 8,900 civilian employees. 
 
 The installation, which encompasses 214,000 acres, is home to two divisions -- the Army's 1st Cavalry and the 4th Infantry (Mechanized). There are 12 other units attached or based there. 

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 By DAVID BARER and CLAIRE Z. CARDONA 
 
 FORT HOOD — A soldier being treated for mental health issues opened fire Wednesday at Fort Hood, killing three people and wounding 16 before fatally shooting himself at the same military base where 13 people died in a 2009 attack, authorities said. 
 
 The gunman was being evaluated for PTSD, but a diagnosis had not been confirmed, said Lt. Gen. Mark A. Milley, the senior officer on the base. 
 
 U.S. Rep. Michael McCaul, R-Austin and chairman of the House Homeland Security Committee, identified the shooter as Ivan Lopez, 34. Fort Hood officials had not formally released his name, pending notification of next of kin. 
 
 Officials said Lopez, a military truck driver, was dressed in his standard-issue green camouflage uniform at the time of the attack. 
 
 Milley said the shooter “had behavioral health and mental health issues.” He said the soldier, who had self-reported a traumatic brain injury and was taking anti-depressants, had been under examination to determine whether he had post-traumatic stress disorder. “We are digging deep into his background,” Milley said. 
 
 Lopez, who was married, served in Iraq for four months in 2011. He had arrived at Fort Hood in February from another base. Police spent Wednesday night searching his apartment in nearby Killeen. 
 
 There was no indication that the incident was terrorism, although the attack was still under investigation and nothing had been ruled out, Milley said. 
 
 “Events of the past have taught us many things at Fort Hood,” Milley said. “We know the community is strong and resilient and know [those] who have served so bravely in combat over last 13 years are strong and we will get through this.” 
 
 Milley said the soldier, who was assigned to the 13th Sustainment Command expeditionary unit, opened fire with a .45-caliber Smith & Wesson semiautomatic pistol that had been purchased recently but was not authorized to be brought on the base. 
 
 Officials believe he walked into one of the unit buildings in the 1st Medical Brigade area just after 4 p.m., opened fire, got into a vehicle and fired from it, got out, walked into another building and fired again. 
 
 He was eventually confronted by a military police officer in a parking lot. He put his hands up but then pulled a gun from under his jacket. “She [the officer] engaged,” Milley said, and then the soldier put the gun to his head and shot himself. 
 
 The injured were being treated at Carl R. Darnall Army Medical Center on the base and at Scott & White Memorial Hospital in Temple, a level-one trauma center. 
 
 Late Wednesday night, Scott & White was treating eight patients, and expecting one more. Three were in critical condition and five in serious condition. All were in the intensive-care unit. The injuries ranged from single to multiple gunshot wounds to the extremities, abdomen, chest and neck. 
 
 First responders, military police and others were on the scene of the shooting within fifteen minutes. The base remained on lockdown for hours. 
 
 Obama ‘heartbroken’ 
 
 President Barack Obama said he was “heartbroken that something like this might have happened again.” Speaking during a fundraising trip to Chicago, he pledged “to get to the bottom of exactly what happened.” 
 
 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.” 
 
 Gov. Rick Perry said in a written statement that Texans’ first priority is caring for the victims and families. 
 
 “Fort Hood has proven its resilience before, and will again,” the statement said. “Texas will support those efforts in any way we can, with any resources necessary. The thoughts and prayers of all Texans are with everyone affected by this tragedy.” 
 
 The shooting was the third major gun attack at a U.S. military installation in five years. A government contractor went on a shooting rampage at the Washington Navy Yard in September, leaving 12 people dead. In 2009, Army Maj. Nidal Hasan opened fire at Fort Hood on a group of soldiers preparing to deploy to Iraq and Afghanistan, killing 13 people and wounding more than 30. 
 
 Except for military police officers, soldiers at Fort Hood and on all other U.S. military installations are not permitted to be armed or to carry privately owned firearms. The restrictions on personal weapons were expanded after the 2009 massacre and an epidemic of suicides at Fort Hood, the largest active-duty armored post in the country. Current policy requires soldiers to register their personal guns with their commanders and to keep the weapons in a secured room. 
 
 ‘Insider threats’ 
 
 Hasan was convicted of multiple counts of murder last year and sentenced to death. He is on death row at the military prison at Fort Leavenworth, Kan. 
 
 Hasan, who worked at Walter Reed Army Medical Center from 2003 to 2006, had been due to deploy to Afghanistan within weeks of the attack. 
 
 Shortly after 1 p.m. on Nov. 5, 2009, Hasan walked into Fort Hood’s Soldier Readiness Processing Center with two guns, shouted “Allahu akbar,” or “God is great,” and opened fire, the court was told. 
 
 Twelve people who were killed were soldiers waiting for medical tests; the other was a civilian who tried to tackle the psychiatrist. Hasan was left paralyzed from the chest down after being shot by an Army police officer and now uses a wheelchair. 
 
 The shootings exposed a number of failings by the Defense Department, which a Pentagon report concluded was unprepared for internal threats, and by the FBI. On one occasion, Hasan had given a presentation to senior Army doctors in which he discussed Islam and suicide bombers and warned that Muslims should be allowed to leave the armed forces as conscientious objectors to avoid “adverse events.” 
 
 In the wake of the Navy Yard shooting, Defense Secretary Chuck Hagel ordered security changes at military installations, including more rigorous screening of personnel and the creation of an analysis center to examine “insider threats.” 
 
 “When we have these kinds of tragedies on our bases, something’s not working,” he said Wednesday evening during a visit to Hawaii. “We will continue to address the issue. Anytime you lose your people to these kinds of tragedies, it’s an issue, it’s a problem.” 
 
 Nerve-racking wait 
 
 Outside the base Wednesday evening, some relatives of soldiers waited for news about their loved ones. 
 
 Tayra DeHart, 33, said she had heard from her husband, a soldier on the post, that he was safe, but that had been hours earlier. 
 
 “The last two hours have been the most nerve-racking I’ve ever felt,” she said. “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.” 
 
 The Washington Post, The New York Times and The Associated Press contributed to this report. 

 FORT HOOD, Texas (AP) — Two U.S. law enforcement officials tell The Associated Press that four people have been killed in a shooting at Fort Hood. 
 
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 Krystina Cassidy, left, and Dianna Simpson attempt to make contact with their husbands who are stationed inside Fort Hood while standing outside of the Bernie Beck Gate on Wednesday, April 2, 2014, in... (Associated Press) 
 
 FILE - In this Thursday, Nov. 5, 2009, file photo, an entrance is shown to Fort Hood Army Base in Fort Hood, Texas. Fort Hood says there's been a shooting at the Texas Army base and that there have been... (Associated Press) 
 
 Krystina Cassidy and Dianna Simpson attempt to make contact with their husbands who are stationed inside Fort Hood, while standing outside of the Bernie Beck Gate, on Wednesday, April 2, 2014, in Fort... (Associated Press) 
 
 A police officer checks drivers' IDs outside the main gate at Fort Hood, Texas, after a shooting at the Army base Wednesday, April 2, 2014. At least one person was killed and at least 14 injured in a... (Associated Press) 
 
 A military police officer stops a car at Fort Hood, Texas, after a shooting on the Army base Wednesday, April 2, 2014. At least one person was killed and at least 14 injured in a shooting Wednesday at... (Associated Press) 
 
 The officials said the four dead in Wednesday's shooting include the shooter. 
 
 One of the officials, citing official internal Justice Department updates, says 14 others were hurt. 
 
 The officials spoke on condition of anonymity because they were not authorized to release information by name. 
 
 The Texas Army 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. 
 
 ___ 
 
 Associated Press reporters Eric Tucker and Alicia Caldwell in Washington contributed to this report.
– Another mass shooting at Fort Hood: Four people are dead and 16 wounded after a shooting at the Texas Army base this afternoon, reports AP. The shooter is among the dead, with initial reports suggesting that he killed himself. The Dallas Morning News reports that the shootings took place in a medical support building about 4:30pm local time, but it's not clear what happened. CNN is reporting that it appears to have started as a "soldier-on-soldier attack" and is not believed to be terror-related. The base was the scene of a mass shooting in 2009 in which 13 people were killed and more than 30 wounded. President Obama, in Chicago for political fundraisers, said he is following the reports closely. "I want to just assure all of us we are going to get to the bottom of exactly what happened,” he said. “We’re heartbroken something like this might have happened again.” Fort Hood ordered everyone at the base to "shelter in place" through its Twitter feed, and that was still in effect into the evening.