The answer to why Marines decided to urinate on dead bodies in Afghanistan could lie in the adrenaline-charged nature of combat and coping with the stresses of war, which can make behavior incredibly unpredictable, experts say.

Then again, the Marines shown in a YouTube video just might be "idiots."

 “These could be pranksters with extremely bad taste, or they could have other, deeper issues, like PTSD. We don’t know,” Eugenia Weiss, a military psychologist at the University of Southern California, told msnbc.com.

A video, which was posted on YouTube, shows men in Marine combat gear standing in a semi-circle over three bodies. It is unclear if the dead are Taliban or civilians or someone else. The title on the posting called them Taliban insurgents and said the Marines were from Camp Lejeune.

'Deplorable': Defense chief condemns urinating Marines video

A number of investigations have been launched, though officials have yet to officially verify the video's origin or its authenticity. Still, no evidence has emerged to doubt what it is.

"It clearly appears to be to us what it appears to be to you — troops urinating on corpses," Pentagon spokesman Capt. John Kirby told reporters Thursday.

It’s impossible to predict how individuals will respond to combat, and why some have difficulty coping and act on inappropriate impulses while others can adapt, said Weiss, who treats Marines near Camp Pendleton.

It is known, she said, that once engaged in war, particularly in places like Afghanistan, heightened adrenaline and increased stress occur.

'Hyper-vigilant state'
“There is this constant, hyper-vigilant state you have to maintain,” Weiss told msnbc.com. “You have an unknown enemy, even a woman walking down the street can be carrying a bomb to blow you up, and you have no green zone, no safe place to get away. This creates ambiguity. And the more ambiguity the greater the stress because of the situation.”

In addition, there is a group dynamic that can kick in among people engaged in close combat.

The act of urinating on the dead bodies “could be a coping mechanism in dealing with a very difficult situation,” Weiss said. “Or it could be this sense of vengeance, because a lot of troops in combat have lost comrades in the line of duty, or even post deployment from suicide or have later died from injuries. So there can be this great sense of vengeance. And that certainly can turn twisted.”

She also said it may have simply "started as a lewd joke, and often times that can get carried too far, you get a group dynamic that kicks in, and perhaps vengeance."

“War-time experiences are traumatic for many men, not only because they are inherently traumatic for all human beings, but also because many men believe they should be able to handle the powerful emotions such experiences create, with little or no personal difficulty,” Michael Addis, a psychology professor at Clark University in Worcester, Mass., told msnbc.com. “Many male veterans are also unprepared for the intense fear, anxiety and personal feelings of vulnerability that can result from combat exposure.” 

At least two of the four men have been identified as Marines based at Camp Lejeune, North Carolina, a Marine official told msnbc.com, speaking on condition of anonymity because there is an active criminal investigation of the incident.

Still, combat stress is no excuse for the behavior, retired Col. Jack Jacobs, an NBC News analyst and a Medal of Honor recipient for his actions in the Vietnam War, told msnbc.com.

"I've been through combat and been stressed out, and I've been out of combat and been stressed out, and I don't think it's a reason or an excuse for this kind of behavior. They've received instruction on how to act and what to do before and after their deployment." Jacobs said. "These are just idiots who are poorly supervised and led ... they proved they are idiots because they took pictures of it."

'Fight to the death'
But for another veteran the video is not shocking at all.

"Many people in this country that worry far more about public relations and how we are perceived by the rest of the world are shocked at Marines urinating on Taliban," retired Army Sgt. Maj. Herb Freidman, an author and authority on psychological operations, told msnbc.com. "Why? They are murderers and terrorists that think nothing of blowing up soldiers, civilians, women and children. What have they done to deserve our respect? There are Marines being killed and maimed on a daily basis by these people. They are flying in from Muslim countries all over the world to get their crack at martyrdom. If some Marine that fought them in battle fair and square feels that he has the right to urinate on a defeated enemy, what is the problem? Hell, it could be worse.... It is a fight to the death, not some sort of gentlemanly duel with seconds and everyone very politely drinking a fine wine afterwards."

Pentagon officials said the criminal investigation would likely look into whether the Marines violated laws of war, which include prohibitions against photographing bodies and detainees and a range of other rules.

“These types of cases are fairly rare, and these are rare circumstances,” Phillip Cave, an attorney in Washington, D.C., who defends service members in court-martial proceedings, told msnbc.com.  “It might be there is more going on, but nobody has put it on the Internet.”

After investigation, Cave said, it’s likely those involved in the incident as well as the person who videotaped it and posted it on the internet will be prosecuted under either administrative or criminal court-martial proceedings.

They could face charges under Article 134, which is the general article on conduct, he said. “In order to establish that you have to have either conduct that’s prejudicial to good military discipline or conduct that’s considered service discrediting. When we talk about services discrediting, we’re talking about giving the Marine Corp a black eye and downgrading the public’s perception of them as good people.

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