Lance Cpl. James Crossan was in the Humvee that was blown up by an improvised explosive device in Haditha last November.
The explosion broke his back and killed his team leader. He suspects that could have been a breaking point for his fellow Marines, now accused of killing 24 Iraqi civilians in the town.
"I can understand, because we are pretty much one family and when your teammates do get injured and killed, you are going to get pissed off and just rage," Crossan said.
And that rage allegedly incited murder.
The rules of engagement on the battlefield are very specific, drawn up for each operation. Every soldier and Marine know it's not just a rule violation. It's a crime to shoot or maim a civilian known to be innocent.
Crossan said in Haditha the insurgents befriended them, and sometimes used children to scout out Marine patrols.
"You can say one thing -- the insurgents, they are getting a lot smarter," he said.
In an unfamiliar country in urban combat, tough situations occur all the time, so soldiers and Marines train rigorously for every possibility.
"We went through scenarios constantly of what could happen over there, and scenarios and the real thing are two different things," Crossan said.
When mistakes do happen, and a U.S. soldier or Marine kills innocent civilians, the law points to one aspect of the incident.
"What matters is their intention at the moment when they pulled the trigger," Columbia Law School professor Scott Horton said.
The Haditha investigations continue, as all U.S. troops in Iraq undergo mandatory core values training to remind them of their professional responsibilities.