this is "nightline." tonight, breaking news. under attack. another mass shooting with multiple casualties at ft. hood, america's largest army base. emergency crews race to the scene. >> take shelter immediately. >> tens of thousands of soldiers and their families are told to take shelter. >> he took the .9 mil and put the weapon to his head. >> who was the shooter? a u.s. soldier and married 34-year-old father. >> he was always smiling and waving whenever i saw him. >> we're outside his home tonight with the neighbor that consoled his wife and child as they heard the news. >> she was shaking. >> a special edition of "nightline." "shooting at ft. hood." we'll be right back.

this is a special edition of "nightline." shooting at ft. hood. >> good evening, breaking news tonight. it has happened again. a mass shooting at a u.s. military base. just hours ago, ft. hood, one of the largest army posts in america, came under attack. in just 15 minutes, at least 16 injured and four dead, including the gunman. the shooter? a u.s. soldier.

a combat veteran. and a married father. abc's senior justice correspondent pierre thomas joins us now. >> tonight our sources are identifying the suspect as ivan lopez, 34 years old. he was an iraq war veteran apparently suffering from mental health issues. and sources believe that played a critical role in the bloody rampage that unfolded today. >> seek shelter immediately. >> reporter: that was the word that first went out late this afternoon at ft. hood. gripped by chaos and fear for hours after a lone gunman opened fired on the army base outside of killeen, texas. home to 41,000 troops. >> it's scary. >> reporter: the shooter is described as active military, a truck driver who was struggling with mental health issues. >> it is believed that he walked into one of the unit buildings, opened fire, got into a vehicle, fired from a vehicle, got out of the vehicle, walked into another building, and opened fire again, and then was engaged by local law enforcement here at ft. hood.

>> reporter: he died at the scene after a confrontation with police. >> he was approaching her at about 20 feet. he put his hands up then reached under his jacket, pulled out the .9 mill, and she pulled out her weapon and then she engaged and then he put the weapon to his head and he died of a self-inflicted gunshot wound. it was clearly heroic what she did. at that moment in time. and she did her job and she did exactly what we would expect of a united states army military policeman. >> reporter: he had served in iraq for four months in 2011. the suspected weapon, a .45 caliber smith and wesson recently purchased in the area, not registered at the base. >> the soldier is married, does have family, and we're in the process of notification. >> reporter: many of those injured were rushed to scott and white memorial hospital in temple. >> they've had a variety of injuries that we've been

treating. ranging from gunshot wounds that involved extremities, abdomen, chest and neck. >> reporter: law enforcement, including the fbi, cleared the base tonight of any other possible threats. while the investigation is still ongoing, there are no indications this was an act of terrorism. no firm motive has been established. but the military tonight made clear the suspect had been in treatment. he self-reported a traumatic brain injury. >> he was not diagnosed as of today with ptsd. he was undergoing a diagnosis process to determine if if he had ptsd. he was undergoing behavioral health and psychiatric treatments for depression and anxiety and a variety of other psychological and psychiatric issues. >> we're heartbroken that something like this might have happened again. >> reporter: president obama pointed out that many of the servicemen and women at ft. hood have recently returned from serving overseas.

>> the folks there have sacrificed so much on behalf of our freedom. many of the people there have been through multiple tours in iraq and afghanistan. they've served with valor and they've served with distinction. and when they're at their home base, they need to feel safe. >> you know, sometimes stuff happens that you just can't control. >> reporter: the shooting today an eerie reminder of the mass murder that played out in 2009 at ft. hood. when army major and psychiatrist in dahl hasan went on a rampage, killing 13 people and injuring 32. it was the worst shooting ever on an american military base. the victims, most of them soldiers preparing to head to war, were gathered for final medical exams when hasan walked in and opened fire. the victims were unarmed and unable to defend themselves. shots were at close range with deadly accuracy. >> stunning. and as i say, as i've gone

around to the hospital here, as i've been at the scene, the soldiers and family members and many of the great civilians that work here are absolutely devastated. >> reporter: a responding police officer finally opened fire, paralyzing hasan from the waist down. last year hasan was found guilty on all 13 counts of premeditated murder and has been on death row at ft. leavenworth since august. since then, there have been at least nine other shootings at u.s. military bases. and last year, a former navy reservist and military subcontractor, aaron alexis, fatally shot 12 people at the washington navy yard. a large portion of the city only miles away from the white house was on lockdown before alex sister was shot and killed. last week a civilian boarded a navy destroyer in norfolk, took a gun from a navy guard, and used it to fatally shoot a sailor before security personnel shot and killed him. all this raising serious questions about security at u.s.

military bases. >> these things are very difficult to stop as far as suppressing all the firearms that could potentially get aboard the base. >> reporter: and what makes this all the more tragic is that it happened at ft. hood, which is still healing from that unspeakable tragedy of five years ago. >> thank you, pierre. but the question remains how does something like this happen at an army base? more specifically, at this army base? we're joined now by abc's chief global affairs correspondent martha raddatz who's reported extensively on the units and families at ft. hood. take us inside what is effectively a small town. >> that's really what it is, dan. it as community. i know we think a military installation, but this is a community. they used to call ft. hood, when i first started going there in 2004, pleasantville. it is kids riding up and down the streets on their bicycles. one of the signs when the men are overseas, when they're deployed, men and women, is the

lone vehicles in the driveway, the empty truck. very poignant scenes when you drive around that army post when people are deployed. and they're deployed all the time, dan. these are two divisions within ft. hood. the 1st cavalry division which i have covered for well over a decade, and the 4th infantry division. those two divisions make up about 40,000 people there, or more. and their families live there on base. when you talk about what happened today and you can hear people say it was miles away, or it was just down the street. there are bowling alleys, there are restaurants, there are kids going to school every day. so you really have to think of this as a community. a community that has suffered so much over the last decade. losing so many soldiers in battle and losing so many soldiers right there at ft. hood. >> and many of them had just returned from afghanistan, correct? >> many had just returned from afghanistan, indeed, including

lieutenant general mark milly who you saw tonight give that press conference. i have spent so much time with lieutenant general milly over the years. i first met him when he was a colonel in iraq so he is someone i know well. and this has to be devastating to him, to his family, to that community in ft. hood. >> i think many will hear that it happens at an army base and say, how can someone with a gun do this kind of damage at an army base, but there are actually rules there with regard to possessing weapons at ft. hood. >> good point, dan. because i think that's also one of those images. people think, well, you're going to an army post, an army base, so there must be people walking around with guns. they aren't. again, it's a community. you have to register those weapons and they are not supposed to be walking around that base with personal weapons concealed on that base. so the military police officer

who confronted the shooter was armed, but he certainly shouldn't have been. in fact, i guess ran back out to his vehicle to get the gun and then went back in and started shooting. >> martha, we know that yvonne lopez was being treated for mental health problems. it turns out you were at the pentagon today talking to them about post-traumatic stress disorder. what do they have to say? >> really quite an extraordinary convince den, dan. i was at the pentagon talking to the deputy commander general of army medical command. and we were talking about post-traumatic stress syndrome and we were talking about how they diagnosed that and how hard that is to diagnose. and he said, well, actually, we still work on this, we still don't know xek how to approach this. but this is an enormous problem in the u.s. military. enormous. i think you have about one in five reporting mental health issues or traumatic brain injury. we have been deployed in this

country, we have sent our troops over there for well over a decade and they have, many of them, come back with issues like this. >> but we learned today that ivan lopez has not officially been diagnosed with post-traumatic stress disorder, correct? >> that's correct. lieutenant general milly said they had not officially diagnosed him but he was undergoing a diagnosis. i think it takes a long time to diagnose someone, whether they have this post-traumatic stress disorder as they call it. but he was under medical care, he was on medication, they said, for depression, for anxiety, and was taking medication for that. >> martha raddatz, always great to have your expertise, thank you very much for joining us, we appreciate it. >> you bet. next, who really was this shooter, ivan lopez? right now our team is just outside his home talking to people who knew him and describing how his wife responded to the news, coming up.

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as we come on the air tonight we are learning more about today's ft. hood shooter. a u.s. army soldier who killed at least three and injured many more. now identified as 34-year-old married father ivan lopez. our team is right outside his family's home and just spoke to a neighbor who was there when lopez's wife learned that her husband was the killer. >> me and a couple of neighbors and daughter were outside and notice the what was going on. his wife came out of the apartment, looked like she'd been crying, looked distraught. i did what anybody else would

do. let her know everything was okay, she need not worry. she told me that she hasn't talked to him since 3:00. she was hysterical. she just sat out here and waited. she made a few phone calls, i guess to family or something. but other than that, i mean -- it was -- it was really dramatic. >> was she shaking? >> she was shaking. she was shaking, she was crying, she couldn't stop crying. >> did she have her daughter with her? >> she had her daughter with her. >> her daughter is 3 years old? >> yes. >> the same neighbor also told us a little bit about what she thought ivan lopez was really like. >> he seemed like a pretty good guy. he was always smiling and waving whenever i saw him. so i didn't think anything strange or unusual. >> we're joined by retired united states army general peter corelly who's served at ft. hood and in retirement has focused on

post-traumatic stress disorder in the military. he joins us from seattle. general, thanks for joining us. before we talk about ptsd i want to ask specifically about this incident. i think a lot of people around the country are going to be saying, are we getting to a point where we have to protect our own soldiers at army bases? >> this is the second incident at ft. hood as we all know. i think we have to be very, very careful to characterize this as anything else than an individual who did a horrible then, for whatever reasons, we don't know for sure. i know general milley indicated the possibility of post-traumatic stress. but again, that's an initial assessment. and i think we have to be very, very careful to jump to any conclusions about this. >> do you think it will lead to changes in security? when people hear that this happens at an army base, some are going to say, is it time to

start having many of the soldiers there walking around with guns, even though that's not the case currently? >> well, i don't think you're going to see that. what really concerns me in an incident like this is the fact that so many people will jump to the conclusion that it was deployment, time spent in iraq or in this instance or someplace else that caused this incident, and they'll in fact brand everyone who's deployed as having some kind of mental issue and that's just not the case. the vast majority of our servicemembers who serve overseas come back and are perfectly fine. >> this particular servi servicemember, though, it seems was being treated for mental illness. he hadn't officially been diagnosed with ptsd. do you think that that problem, and you say that it may not be that widespread, but is it widespread enough that the military isn't doing enough to address it? >> well, the military's doing more than anybody else to

address it. i think the army alone spent over $500 million on medical research into post-traumatic stress. in the last six or seven years. the problem with post-traumatic stress, and the general public i don't think understands, is this isn't like having a broken leg and going in and being x-rayed and saying, yes, your leg is broken. it is extremely difficult to diagnose with any accuracy. and that's not just true in the military, that's true in civilian life. >> what more do you think can be done to address the issue of mental illness in the military? >> well, i think we need to address the issue of mental illness in society. i really believe that it is absolutely imperative that we put the necessary funds, and we get people to work together and share data and information, researchers, to try to get at these issues. that to me is what really needs to be done. this ought to be a wakeup call

not just for the military, but for all of american society. to get at this problem. >> general corelly, thanks so much for joining us, really do appreciate it. the latest breaking details on today's fatal shooting at ft. hood coming up. ♪ [ engine turns over ] [ male announcer ] the 2014 nissan altima. with 270 horses... ♪ ...blind spot warning... ♪ ...and advanced drive assist. ♪ nothing beats an altima. except another altima. ♪ nissan. innovation that excites. ♪

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more now on our breaking news story. a gunman at ft. hood fired around 20 shots, some of them fatal, at america's largest active duty army post. with eerie similarities to a shooting in 2009 there, the spire base took shelter as emergency vehicles raced to the scene. the gunman was 34-year-old ivan lopez who was being evaluated for possible ptsd after serving in iraq. he used a .45 caliber semi-automatic weapon that had not been registered at the base to kill three people and himself today. 16 more were left with injuries ranging from stable to critical condition. our thoughts and prayers are with those at ft. hood and their families tonight.

now we go back to pierre thomas. what happens next in the investigation? >> well, dan, as we speak they're dissecting this man's life. they're talking to friends, associates, trying to get a sense of who he might have been communicating on e-mail, on the internet. they want to know everything about him. they want to make sure he has no ties to domestic terrorist groups, international terrorist groups. there's no indication of that, but they need to know everything that they can know about him. but the central focus appears to be right now on his mental health. all that he was going through. all the issues with the medications and the treatment that he was getting. what was the thing that set him off? that's what they want to know. >> it was interesting to hear the general in the press conference say he didn't think there was a fight that precipitated it but it does seem they're continuing to investigate that possibility as well. pierre thomas, thanks very much, we appreciate it. stay with abc news for the latest on this developing story. we're always online at abcnews.com. "world news now" is coming up soon. "good morning america" will have

a full report tomorrow. good night, thanks for watching.

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