Sorry to hear of your loss, that's truly tragic. You have our support and sympathy.
Blind, unbridled rage is the dominant emotion I experience when these attacks take place. We've had several incidents in the last couple of years in Calgary involving serial dog poisoners. From what we've seen here, the best way to catch these people is to inform the neighborhood of what's taken place and watch for the culprits try the same on another dog.
I personally feel that the perpetrators should be staked to the ground and a pack of ravenous hyenas turned on them.