What kind of dog was it?
I'll assume she was inside a gated area at all times. Has anyone ever complained about her being aggressive? Were their any tenants that were less than happy with the 'guard dog'? There are a few questions to ask here to determine why someone would have done this.
I am only saying this - dog owners view their aggressive dogs with rose colored glasses, passersby and neighbors view it thru red tinted glasses. Loose dogs and/or nuisance barker dogs can destroy neighborhoods. Even though you thought your dog was sweet, odds are there are more than a few neighbors breathing a sigh of relief at the silence now. No offense meant to you, and I definitely don't believe in harming animals. However, history shows that once it gets to a point of killing the animal, the situation is much worse than you think it is for other people.