Apparently the video showed the Marines discussing whether or not to give an injured insurgent first aid, the video ended shortly after and the insurgent eventually died. So I'm guessing they didn't give him first aid and he died as a result of that alone.
Now 5 Marines have been charged with muder? What a joke!
considering under the rules of engagement and the Geneva convention, you are supposed to give first aid to captured enemy combatants, so yeah they broke some pretty serious rules there, deserved if they get found guilty.