Trivia: At the end of the movie, the plane is crashing into the front of a casino. This building is actually The Sands hotel. The scene was done a few weeks/months before the hotel was demolished, this way the damages to the hotels entrance as the plane was launched into it didn't matter.
Trivia: Dave Chappelle ad-libbed most of his lines.
Trivia: The original plan for the ending of the movie was to crash the plane into the White House.
Trivia: The scenes of Garland Greene and the little girl were added to give him more screen time. They filmed them after principal photography was finished.
Trivia: John Cusack hates this film so much, he refuses to talk about it in interviews.
Chosen answer: Zero. As you said, he was attacked and there are witnesses that he tried to avoid the fight and the killings were in self-defense. It is an extremely weak plot hammer to get Poe onto a plane full of criminals. It's foolish as well. The writers could have had Poe framed for a crime then exonerated and put in the same situation much more believably.
Grumpy Scot
It's in Alabama. People are put in prison here for much less.
First, Poe is a federal prisoner, not subject to State laws or legal procedures. Secondly, he is not in Alabama. During a conversation with Billy Bedlam we hear that he is incarcerated in the "Q" - prison slang for San Quentin in California. It makes you wonder why a Federal prisoner is in a State prison, but that's another type of mistake.
Would it really be considered self-defense, though? After he beat the guys to the ground he could have just stopped and walked away, but he didn't. He kept beating them until they died.
He is defending his wife against two armed assailants, and use of lethal force is allowable. No DA in the United States would even think about pressing charges, knowing full well a grand jury would throw them out in a second.