You did say that, or rather implied it. You claimed this person must know every single cop, but you just admitted right now that actually you don't need to know every single cop to prove that all cops commit crimes. Because covering up for someone else is also a crime, and all cops presumably cover up. Arguably, just the simple act of existing as a cop is perpetuating injustice of the system.

So it's sort of self proving, or proven by definition. By definition of what cops are and what they are allowed to do, all cops must be bastards. If they weren't, they wouldn't be cops!