A 30 year cop (presumably) isn't going to spend the ENTIRE career working as a beat cop on the graveyard shift in the worst parts of Baltimore or Chicago. They

A 30 year cop (presumably) isn't going to spend the ENTIRE career working as a beat cop on the graveyard shift in the worst parts of Baltimore or Chicago. They also rank up and/or change positions to be detectives, special investigations, expert witnesses for prosecutors, bosses or administrative police staff. Meanwhile SWAT details (particularly in medium sized cities with more toys than mandatory training) are going to consistently attract the worst of the so called "bad apples" from the greater ranks of police. Individuals that joined up specifically because the rough and tumble stuff appealed to them.