"A common trope amongst police officers in the United States is the aphorism: "If you lie, you die." This is indicative of the essential need for trustworthiness in the job—police officers are society's observers, enforcers and professional witnesses—and a warning that any deliberate falsehood can undermine the officer's continued usefulness, resulting in termination. Such terminations have been judicially enforced.[20]"
I personally know of 3 cops who lost their job for dishonesty. It's not even stuff like planting drugs, but turning in fake tickets (court copies never submitted, just office copies).
Further, look up the Brady List. In everywhere I've worked, if you're on it, the Commonwealth's Attorney will not take your cases. Period. If your lawyer loses a case where the witness is a cop who has lied intentionally on record, you have a crappy lawyer or a terribly corrupt judge AND jury