Man, sometimes people are just stupid. I used to be a police officer myself, but that is just nuts. I would have told you to go for it. Inhumane? A bullet to the head might be humane to a degree, but not as humane as a CO2 chamber, not to mention that any time you fire your weapon their is a possibility of liable should anything go wrong.

Granted I had to put down several animals while I was a police officer, it was not something I enjoyed much, but things like that have to be done sometimes.