A gunman at ft. Hood fired around 20 shots, some of them fatal at America's largest active duty army post. We'rery similarities to shooting there in 2009 left 13 dead, the entire base took shelter as... See More
A gunman at ft. Hood fired around 20 shots, some of them fatal at America's largest active duty army post. We'rery similarities to shooting there in 2009 left 13 dead, the entire base took shelter as emergency vehicles raced to the scene. We now know the gunman was 34-year-old Ivan Lopez who is being evaluated for possible PTSD after serving in Iraq. He used a 35 caliber semiautomatic 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 ABC's chief justice correspondent 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. They're 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 group, 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. Thanks very much. We appreciate it.
This transcript has been automatically generated and may not be 100% accurate.