The writers, Andrew Rule and John Silvester, say
For every psychopath who pulled the wings off butterflies and tortured kittens on the way to his corner of hell, there are plenty of hard men who would happily break (human) bones to punish cruelty to animals.They give the example of the murder of Les Kane in 1978. When the Kanes came home from a restaurant to the house where they were hiding out from their enemies, their dachshund, Simon, was on a chair beside the front door - a chair he was not capable of climbing up onto. One of the three masked killers (who then pushed Mrs Kane and her children into a bedroom before shooting Kane and taking away his body) had apparently let the dog out and put him on the chair out of harm's way while he waited to commit murder.
Another story is about a man called Bazley who was hired to kill two people involved in the drug scene, in 1979. He was ordered to kill their dog, but he didn't, instead turning the dog loose. He later said he wouldn't shoot the dog because it hadn't done anything wrong.
And on one occasion another man was saved from a sharpshooter on a roof because he noticed his companion dog was staring out the window at the roof of the house next door.
There are more stories in this interesting article, but I'll let you read them for yourself if you want to.