Fdzzaigl said:
Calm or not calm, shooting the dog was the best option given the situation.
If they attempted to capture the dog:
Dog was agitated, could bite or maul officer, if capture failed dog may run into crowd of civilians and injure one of them.
Pepper spray: Further agitate, inflict pain, and disorient the dog causing it to be even harder to handle, greater chance of injury to officers or crowd.
Taser: Again further agitate and inflict pain on dog, higher chance of injury to officers/civilians, see article on the unpredictability of tasered animals: http://www.abc4.com/content/news/state/story/tasing-dog-shooting-dog-dozer/SO0rZUC9Ek6dlXuzvZCVGw.cspx
Release cuffed individual to handle animal: Individual was already acting erratic, would have taken too long and there is no guarantee he will compile and restrain dog (as he had already failed to do so previously), possibility he may run or command dog to attack.
Shoot dog: high chance of success, no injury to officers or civilians, however does result in death of dog.
While no one can say what state of mind the officer was in while shooting the dog, its clear he made the correct choice.