This is such a shame. I've always thought about things like this happening because of how crazy some people are, especially in regards to religion. I could easily see how this could happen in a JW Hall with the mental anguish and turmoil from shunning and strained family relations, especially when the person already has a mental illness.
I realize that this is most likely a racially motivated hate crime, so it's a little different than the above scenario. Anyways, my heart goes out to the families that have lost. They went to church to find peace and security in their God, but he did not protect them. Sadly, the families will be turning to God for comfort thinking this must have been part of God's will to get a few more angels.