“b. You don’t leave department property laying on the ground where you can’t keep an eye on it and some bystander can walk off with it.”
Nonsense. As soon as the officer fired his weapon, the location became a crime/investigation scene. You don’t move evidence in a crime scene simply because you don’t want to leave department property on the ground. If you are worried that a bystander will walk off with it, then keep an eye on it (or have someone else do the same).
Spend much time at crime scenes? Stuff that has no evidentiary value gets moved all the time. Moreover, all there is is an assumption that what he picked up was a taser. Coulda been the guy’s shoe, or wallet, whatever. More reason to wait for the facts to emerge rather than invent an evidence planting claim.