Professor Don B. Kates, Jr., eminent civil rights lawyer and criminologist, states:
Even if all 500,000 American police officers were assigned to patrol, they could not protect 240 million citizens from upwards of 10 million criminals who enjoy the luxury of deciding when and where to strike. But we have nothing like 500,000 patrol officers; to determine how many police are actually available for any one shift, we must divide the 500,000 by four (three shifts per day, plus officers who have days off, are on sick leave, etc.). The resulting number must be cut in half to account for officers assigned to investigations, juvenile, records, laboratory, traffic, etc., rather than patrol.