When police caught up with alleged killer Eddie Ray Routh last weekend, the 25-year-old ex-Marine was crying, shirtless, shoeless and smelling of alcohol.

Not long before, at a Texas shooting range, police say, Routh had gunned down Chris Kyle, the Navy SEAL who called himself America's deadliest military sniper.

As he sits in a Texas jail cell, details about Routh's psychological make-up have surfaced, including claims that he suffers from post-traumatic stress disorder, a condition that affects a number of current and former members of the U.S. military.

Of course, combat duty doesn't automatically lead to PTSD. And it's not even clear that Routh served in a combat zone during his four years in the Marines.

Nonetheless, Kyle's tragic death and Routh's story are shining light on those who suffer from PTSD and the circumstances that surround it.

Here are five things to know about PTSD:

What is it?

Anyone who has experienced a life-threatening situation can develop PTSD, according to Dr. Stephen J. Cozza, a professor of psychiatry at the Uniformed Services University of the Health Sciences. A sufferer typically re-experiences the trauma through flashbacks and nightmares, experiences that can seem as real as the actual trauma. The person often feels intensely that the trauma could happen again at any time.

How common is it for someone to be diagnosed with PTSD?

While many people will have extremely distressing or threatening experiences in their lifetimes, only a small percentage will experience PTSD, experts say. In the general population about 7% of people experience PTSD, and there is a 60% chance of at-risk individuals -- combat veterans, victims of natural disasters or victims of violent crime -- experiencing PTSD, according to Dr. Albert "Skip" Rizzo, a psychiatrist who works with the military and has pioneered use of virtual reality for treating PTSD.

Thirty percent of service members who have fought in Iraq or Afghanistan have been diagnosed with PTSD, according to a Department of Veterans Affairs study released last year.

"We need to remember that while substantial numbers of vets have mental health conditions," Cozza said, the majority do not.

"We don't want to stigmatize our vets, because many of them are not ill," he said. "As an organization and as a community, the military has varying levels of health and risk. There are more services for mental health care in the military than there has ever been before."

Could PTSD lead someone to act violently?

There's no way to answer that definitively, experts say. But new research is being conducted.

Iraq and Afghanistan veterans who struggle with anger are twice as likely as other vets to be arrested for crimes, according to the Journal of Consulting and Clinical Psychology, which published a study last year.

The study, conducted by the University of North Carolina-Chapel Hill School of Medicine, examined 1,388 combat veterans. Researchers found that about 23% of those with PTSD and high irritability had been arrested for criminal offenses.

But researchers also found that other factors unrelated to military service -- including growing up around violence or drug abuse -- were factors behind why some vets committed crimes.

Is there a way to treat PTSD that lessens that chances that a sufferer will act out?

Exposure therapy often helps the person with PTSD revisit or re-experience their trauma as a means of lessening the effect the memory has on them, said Rizzo, who is with the Institute for Creative Technologies at the University of Southern California.