It is a police officer's duty to secure one if he can do so by legitimate means.

It is his custom to secure one by any means in his power.

As his oath, that such a statement was voluntary, makes it ipso facto admissible as evidence, the statutes providing that a defendant cannot be compelled to give evidence against himself are practically nullified.
In the more important cases the accused is usually put through some sort of an inquisitorial process by the captain at the station-house.

If he is not very successful at getting anything out of the prisoner the latter is turned over to the sergeant and a couple of officers who can use methods of a more urgent character.

If the prisoner is arrested by headquarters detectives, various efficient devices to compel him to "give up what he knows" may be used--such as depriving him of food and sleep, placing him in a cell with a "stool pigeon" who will try to worm a confession out of him, and the usual moral suasion of a heart-to-heart talk in the back room with the inspector.
This is the darker side of the picture of practical government.