WAG? I'd say for some people the fact that she was a cop means an assumption of professionalism and deference to her judgement in the case. Amber the bartender was just a trigger-happy redneck with no training looking to blow someone away. But if a cop went to the wrong apartment and shot the occupant, well there must have been something done to her to cause that mistaken entry and surely a cop wouldn't have shot someone without cause, so he must have done something to deserve, or at least cause, it.
I say this as someone with generally a strong pro-law enforcement bias. I think the fact that she was a cop has some people wondering what he did wrong to make her shoot, since she must have had a good (even if flawed) reason for her actions, her being a professional and all.
Personally I don't buy an inch of that reasoning.
She is a cop who had previously shot a suspect with at least some justification, but also she was the only police officer to actually think it worth shooting in that case, which suggests she's a bit more trigger-happy than most other cops.