Yes, the documentary is on youtube and other places. It is "The Mexican Mormon War" and is very informative. I thought I had posted that in an earlier post but the post was deleted. (Mods, it may be too much effort to do this, but if you delete one of my posts, you are welcome to PM me to let me know where I went wrong without upsetting me.) Perhaps my link wasn't allowed? Perhaps, I didn't complete my post.
In any case, the Mormons in Mexico have been in conflict with the cartels for many year with violence escalating for the past ten-or-so years. Two members of the LeBaron family were murdered in 2009. This latest incident is a continuation of this conflict.
Oh, well, Wikipedia will tell you more if you are curious. The documentary will tell you more and watching it is vitally important to understanding the context of this latest tragedy.