Silky Terrier and Bullmastiff got in fight,my Silky died after $4000 in bills. Who is liable? Read for detail!

I was walking my 7 year old Australian Silky Terrier near a lake, off the leash. 20 minutes into the walk, a large Bullmastiff came charging from around a bushy area (this was a bush walk area where there is a lot of space and water, like a basin or dam) and knocked my Silky (male, named Benny) over and started a fight with him. As Benny was an older dog and he was already suffering of very MILD elbow dysplasia that he had had since he was 4. The Mastiff was off the leash, had no collar or muzzle and was very aggressive. I did try to seperate Benny and the Mastiff but as the dog was well over 100lb, I was scared for my safety. The owner finally came running to see what was going on as I was yelling. He was holding a leash with a Bulldog pulling on it. I took Benny to an ER (this was last week) and $4283.98 in vet bills later, Benny died. Am I liable to pay this or should I be asking the other guy? How much is he liable to pay? What else is am I or he liable for? Please help!I understand my dog was off the leash but we has not running in front of me nor was he barking or pulling any attention to himself. I am very emotionally distrought after watching my dog die right before my eyes and seeing this massive dog attack my dog who was around 9 inches in height and approx. 10lb in weight compared to a large Mastiff. I can not afford to be over $4000 short, money wise, as my father recently passed away and I need to pitch in money with my siblings, my mum and other family members to pay for his funeral. How much is he liable to pay? How much am I liable to pay? Is he liable to any other charges? Am I liable for any other chareges? Please explain how this will work!He did give me a phone number and a name but he wants vet bills and proof that he owes me anything. He thinks I should have paid more attention, my dog should have been wearing a leash and a muzzle as my dog did bite his Mastiff on the ear. Please help me!He has already sent me a bill of $575.42 (which is the WHOLE bill) and expects me to pay ALL of it. He says that his dog was very affectionate, loving, caring and wouldn't hurt anything at all.This is entirely wrong. His dong CHARGED from around a bushy area and attacked my dog without a peep. FYI: After a 20 minute walk in the basin, I had never seen the dog before. I was on my way home (I live approx. 10 mins away from the basin/park) so I took the leash off him like I always do after our walk. He always wears the leash and sometimes a muzzle (as there are sometimes rodents running around there and Benny loved to chase them) while we are walking in the basin/park. I have told him to pay 3/4 of the vet bill and he refuses to pay more than $500 which is around 1/8 of the vet bills in total.Oh and he also wants an additional $180 (on top of the $575.42) for emotional distress of seeing a dying dog. What's up with that?!And $206 for missing 2 nights of work as he had to stay home with his dog to make sure he recovered properly. So that's around $1000 for bills, emotional distress, work etc. that he wants off me when I can't get more than $500 off him without going to court!Raysin: That's what I was thinking. After a 45min phone call last night and a 3 page letter from him (2 nights ago), that's what he wants off me.