Mass murderers sometimes masquerade as authority figures to gain compliance from their victims. It’s becoming especially common with home invasions, as those are almost indistinguishable from police raids to the residents.
Sometimes the murderers are police officers. The respect or fear of the uniform gives them an extra margin of safety from defensive actions of their victims and from the eventual response by legitimate police.
In short, it’s not enough for a peace officer to look the part. Actions speak louder than words and reflect on the entire agency. I’ve seen both kinds and found the local cops to be mostly lawful good. What kind of police does your town have?