Internaler Affairs?
Seriously though: The cop fucked up hard: He shouldn't have approached with his gun drawn, if he felt like he needed to go in armed he should have asked for backup unless he had cause to believe that unless he had cause to believe he needed to act NOW, which by all appearances he didn't have. He should be punished for not following proper procedures, possibly losing his job in the affair.
On the other hand, shooting a strange dog running towards him in a manner that can be interpreted as hostile (do note that as far I as I'm aware cops are not required at being experts in reading dog body language) in a context that he thought might involve violence? That I can't really recriminate him for. They should bust his ass for the whole rest, not for the snap decision of shooting a dog, tragic as it may be.
On a sidenote: The command to control the dog was probably meant something like giving a command for the dog to go back home/or come over, not actually physically restraining the dog, and so actually possible to do at the same time he was raising his hands. Not that the cop have not breached protocol hard by going with a draw weapon or and/or getting backup
