I found a website that deals exclusively with church violence, Church Crime History. I do not know this person so I'm not endorsing it but he has a lot of information and statistics. I believe that his purpose (and mine, frankly) is to make people aware that churches can have violence. Information is always good - information can be used to help members be more aware of what is happening in other churches. Share this resource with whomever you feel it would help to know about this.
Let me encourage church leadership to take some pro-active steps for safety and security. The depth of those actions is dependent on the church's budget and the perceived potential danger to the church and its people. Some actions won't cost the church a dime (such as setting up a Safety Officer Team) while others are much more expensive (such as security cameras). It is true that many of the items listed in Church Crime History could never be prevented - no argument there - but some precautions are always a good step in the right direction.