His rampage left eight people dead before he turned the gun on, and killed, himself.
Psychiatrist Dr. Harold Koplewicz, director of the Child Study Center at New York University Medical Center, told co-anchor Harry Smith on The Early Show Friday, "It's very troubling that we have to have a terrible event like this for us to discuss this. Let's take this in context, though.
"The good news is most psychiatrically ill young adults do not kill people, do not have violent episodes, and even don't kill themselves. However, the psychiatric illness itself really damages them. But it does happen. So, every year in this country we lose 5,000 kids to suicide. Between 14-and-24. They kill themselves. This (incident in Omaha) is a suicide, also.
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"And depression is the No. 1 reason people kill themselves. And we do see warning signs of depression at least two years ahead of time. People suffer a very long time before they ever come to our attention. So, there are warning signs."
Depression, Koplewicz says, is "definitely on the rise, but I think, most importantly, that Americans have to recognize adolescence, which does occur between 13-and-24, is the prime time for when you're going to get depressed.
"We're not talking about demoralization. We're not talking about bad things happening. But it's much more common during adolescence than it is during childhood or adulthood. When you become very old, a geriatric, over 65, a whole different problem.
"So, during adolescence, there are 2 million people who have depression. Out of those 2 million, some of them get very sick. This year alone, we'll have 600,000 teenagers who will try to take their lives and will need medical attention.
"Just think of it from an economic point of view. Forget about the humanity of it. They will need a tremendous amount of services from an emergency room. So, this is a real public health problem that we have to address. Parents and educators have to understand what are the warning signs of depression."
If parents see signs, what should they do?
"First thing, go to your pediatrician or family practitioner. Find out if it's a virus, a flu, if it's physical. If not, if it's depression, you have to get it treated. Treatment works, and then you have to make sure the kid takes the treatment. Remember, when you were a teenager, you wanted to be the same as everybody else, and the last thing you want to do is be sick. But if you leave these kids untreated, these diseases, particularly depression, it only gets worse. It doesn't get better.