Wow! This sounds amazing! I'm all into writing stories (and I'm good at it). Since the story is very unusual, I think I'm gonna need a lot of details so that we can make a very interesting (and enjoyable story). Great part of the writing will be in the details. Unless it's going to be a fiction book, based on real events, then I'm sure I can make a great story out of that. If it's some kind of chronicle, I'm going to definitely need a lot of details so that we can have a very rich text.
I don't know why these two gangs played this game. Was it some kind of truce? Or that's how they solved some issues? Either way, the motivations for this game (and of course its outcome) could be such an interesting story to tell, as I'm sure you're aware of.
I live in Mexico City, and there's a chance I can travel to El Paso (if needed for gathering all the data). Which also could be done long distance if that's your intention. I'm willing to write a short story before hiring, so that you can see my writing style.
I think this is a very exciting project and I'd love to give it a try!