Mixing up your taser with your handgun

[HappySkeptic]

But confusing a less-than-lethal weapon with a lethal one may be a sign that this person shouldn't have been a cop to being with.

Boru

Sure, that's true.  If the cop was under that much stress for a simple situation, they probably shouldn't be a cop.  But mistakes during stress are a very real thing.  During periods of tunnel-vision, the brain can ignore the feedback of things like "why is my taser feeling a bit weird?".

So, yes it is reasonable to believe that someone can make a mistake.  It is either that or cold-blooded murder.  There is no "accidental discharge".