sry to be a pedant but that's not what Hannah Arendt (who coined the phrase) meant by banality. She meant stupidity, the stupidity of evil. She likened it to becoming an insect, that evil behavior dehumanizes the person behaving that way by reducing their mental output to that of a bee or other animal that does things routinely without ever questioning it or deviating from it. You become banal by just doing what everyone you is doing and rationalizing it to yourself as being okay until you no longer need to rationalize it at all, even that becomes automatic and robotic.

Somewhere down the line, "routine is evil" got flipped in the public mind into "evil is routine", but she very much meant the former, not the latter. OP's policeman would fit that definition, but not the average sex offender.