This agent should be relieved of his badge until a thorough investigation into his fitness for the position can be 100% determined.
Also; he should not be allowed to carry a gun until his mental fitness can be determined.
Quick check of the facts: An off duty agent turns a corner, a uncontrolled Belgium Malamute charges at him, he draws and fires a single shot at night into a smaller than man sized target. Let's see.. 100% on the shooting test, 100% on the vision test. Seems fit for duty to me. Six week paid vacation while the shooting is investigated by the NYPD. Keyboard warriors go wild...
As for the leash being in photos - many people will carry the leash while walking their 'well trained dog', could have been on the dog when it was running wild or could have been put on by the owner after the dog was shot.
Had that been one of the few concealed carry permit civilians in Brooklyn, the investigation would have been wrapped up already.