To you and everyone else who is assuming this happened in Iraq - please read the article. Apparently, this happened in Hawaii. Hardly a war-torn, stressful environment.
These guys should be court-martialed - period.
Here's the first sentence. "The U.S. military are investigating a shocking video of a smiling Marine throwing a puppy off the top of a steep hillside in Iraq into a gully below."
I'd suggest that you follow your own advice.