It is equally hard to police a city of a million or so polyglot inhabitants with a due regard to their theoretic constitutional rights.

But suppose in addition that these theoretic rights are entirely theoretic and fly in the face of the laws of nature, experience, and common sense?
What then?
What is a police commissioner to do who has either got to make an illegal arrest or let a crook get away, who must violate the rights of men illegally detained by outrageously "mugging" them or egregiously fail to have a record of the professional criminals in his bailiwick?
He does just what all of us do under similar conditions--he "takes a chance." But in the case of the police the thing is so necessary that there ceases practically to be any "chance" about it.

They have got to prevent crime and arrest criminals.

If they fail they are out of a job, and others more capable or less scrupulous take their places.

The fundamental law qualifying all systems is that of necessity.