We still want to know more about this gunman with a history of depression and anxiety. So, ABC's chief global affairs correspondent, Martha Raddatz, who has covered the community of soldiers at ft.... See More
We still want to know more about this gunman with a history of depression and anxiety. So, ABC's chief global affairs correspondent, Martha Raddatz, who has covered the community of soldiers at ft. Hood, for years, tells us what she's learned tonight. Reporter: Ivan Lopez spent nearly half his life in the army, serving as a peacekeeper in the sinai, infantry man in the deserts of Iraq. First joining the guard in his native Puerto Rico, where his former supervisor, today, had nothing but praise. So, you would say he was an outstanding soldier? That's correct. He was an outstanding and disciplined soldier. Reporter: But now, we know that last summer, things began to unravel. From depression, to anxiety, to some sleep disturbance. He was prescribed a number of drugs to address those. Reporter: Including ambien, for sleep. And while he saw that psychiatrist, as recently as last month, no signs of what was to come. And even though Lopez was being tracked for signs of posttraumatic stress, he had not been diagnosed and fully treated. There's not a diagnosis that you make on one department. Reporter: Even if he had, it's unclear whether he would have stood out. The military, today, dealing with a staggering number in its ranks. One in five, with mental issues. More than double the civilian population. Almost always, it's about depression, not violence. Depression, anxiety, PTSD, those are on the mild end of the scale. Reporter: This happens just as a time when the army is trying hard to destigmatize those who report symptoms of posttraumatic stress. But the military is trying to keep up with the number of cases. A number, Diane, that is sure to grow. Thank you so much, Martha Raddatz. And ABC senior justice correspondent, Pierre Thomas, is standing by, with the latest on the investigation. Pierre? Reporter: Diane, law enforcement is now dissecting every part of Lopez's life. They are looking at reports that he got into a heated argument on the day of the shooting. They are going through his computer, Facebook page, e-mails, anything that might shed light on why he snapped. One area they may focus on. His family in Puerto Rico tells us he was extremely upset about given a limited time to return home after his mother died of a heart attack last November. Diane? Pierre Thomas and the entire ABC news team on the story tonight.
This transcript has been automatically generated and may not be 100% accurate.