They were called in by the owner of the trailer park to capture wild dogs and cats
They encounter a dog running around without a leash or any supervision
They capture it, as instructed by the landlord, who owns the property
The only thing they really did do wrong was not wait the mandatory 5 days before they put the dog down.
But the reality is: If you’re running the only animal shelter around that won’t turn away animals, you’ll be forced (by law) to euthanize a lot of them. What else are you going to do? You can’t just let the animals loose, no one else will take them and more are coming in daily.
PETA is catching flak for carrying out the consequence of people breeding and then abandoning dogs, which is the real crime.