You're a fucking moron. Yes, chain up the god damned dog if the owner doesn't have a fenced yard. People's pets should not be roaming, period. You'd probably be tearing the owner a new asshole if this dog attacked a person or got hit by a truck.
I own both dogs and cats, the dogs only go outside unsupervised in the back yard with an 8ft privacy fence. The cats never go outside.
I also don't have a problem with cats killing birds and squirrels. Birds are disgusting animals and squirrels are just rodents.
Feral (and OUTDOOR cats) often kill rare and or protected species of birds which sucks on two levels, first birds eat bugs, lot's of em without birds the insect population would explode, second, some birds are on the verge of extinction due to habitat destruction and cats. OP, sorry about the loss, feral or not you were attached to this animal and it sucks to have it killed like that, I hate asshole dog owners who are in their front yard with their dog unleashed, I'm walking my dog (on a leash) when they run out after us, usually with the owner screaming at it to STOP!, COME! which EVERY dog ignores and confrontation ensues. Unless your dog is inside a fenced in area it has NO business being off a leash whatsoever..