<human>: Background: Victoria, Australia

About two months ago I was sitting in my loungeroom watching some TV when I hear a pretty sickening yelping from outside. I dart outside to find a neighbors dog (pit bull) holding my dog (whippet) by the throat, doing a pretty good job of messing her up and coming really close to killing her. My backyard isn't completely fenced off, but our dog's don't venture out to the front yard and more than half of the property is walled from the house to the fence, if you follow. 

I convinced the owner of the house the dog came from to pay for the bill, but his son (who owns the dog) is a dropkick to put it kindly, and has a violent and colorful history with the police for stabbings, robberies etc. 

Fast forward to yesterday, and I'm walking my dogs down the street. The same dog charges out of their property and latches onto one of my dogs, only releasing it when I belt it repeatedly with a stick. The owner of the house runs out and pulls his dog inside, and is nothing but apologetic, but his son runs out and throws me to the ground, launching all kinds of threats and verbal abuse. He basically tells me that if I report his dog or get him into any kind of legal trouble - he's going to 'pin your f##king dog's to the shed wall and burn down your house'. 

I've put the vet bill in his letterbox, dolled it up to look like a regular letter and addressed it to the house owner. I don't doubt he will avoid the fees, it's a hefty fine to have a dangerous dog and I made sure to let him know.

The question is, what else can I or should I do about this dog? I want the mongrel put down, but I don't want to endanger my pets or family / home.

Can you summarize the given text in a few sentences?
<bot>: Dog has attacked my dogs twice, in my yard and in the street, owner has a history of violence and crime and has threatened repercussions if I report him or his dog.