Wrong? It would create an unethical conflict of interest, that the judge wouldn’t allow. So in that sense it would be wrong.

Immoral? Not if they genuinely gave the cop the best defense possible. In fact, I’d think it honorable for someone to uphold their principles even against the personal pressure they’d be feeling from much of their family.

It’s important for people to have protection from a system that’s too often used to abuse. Even if the accused was formerly one in a position to abuse.

Principles aren’t principles if we don’t uphold them when it’s most difficult to do so.