This was a super bad choice and the cop (and whoever made the decision if it was someone else) needs to be held accountable. Animal control (which doesn't even always exist) is usually stretched super thin and only covers certain areas (for instance inside city limits). If it was necessary to bring the snake down and if it was dangerous then they should have done it differently, or at least more carefully.
When there was a rabid (or just insane) raccoon terrorizing my gf's dog and back yard guests we called everyone to get some help with it, but there was no official assistance available to her. So I called county dispatch to let them know I was going to be shooting it and to disregard any phone calls about gunshots. Then I had a couple of our guests go door to door around us to let the neighbors know there was about to be gunfire. I climbed onto the roof so that I could get a downward angle on the shot (the my excellent compatriot was up a tree at the time). I took the shot braced on the chimney stack so that I could be as stable as possible.
First shot from my 3 1/4" carry pistol took it halfway between the left eye and it's nose, dropping it out of the tree. I looked over the edge of the house and saw it trying to writhe away so I took a second shot and put it through the spine at the base of the head, killing it outright. Those shots were about 20-25', and 15' away, the second at a moving target, with a short barreled pistol - and I hit within an inch of where I was aiming both times.
Granted, I'm a good shot, but the cop in this incident should have been at least as careful...especially if he wasn't sure he was that good of a shot. It's certainly possible to shoot a snake out of a tree with a handgun, but take some precautions. No, bad choices all around, and they should be liable.