IN a place of deep despair – the medium-security Luther Luckett Correctional Complex in Kentucky – a group of inmates are turned into theater people. Haven’t they suffered enough?

The documentary “Shakespeare Behind Bars,” which is aimed at that audience inclined to believe that prisoners don’t really deserve to be locked up, especially if they seem nice or had lousy childhoods, follows the inmates as they rehearse for their annual Shakespeare play, in this case a production of “The Tempest.”

The Shakespeare program was designed by a hopeful warden to help prepare his prisoners for society again. But “this ain’t Mary Poppins,” warns one criminal, noting that any moment you could lose a cast member to “the Hole,” which sounds even worse than off-off-Broadway.

The inmate-actors are huggy and sentimental, though it seems likely that the program draws these kinds of personalities rather than creates them. There are moving moments, and surprises: I wouldn’t have guessed that you could find so many inmates who are comfortable using words like “ingenue” and “usurped,” and these men are really dedicated to learning their lines as well as interpreting the meaning.

Working on digital video, the filmmakers also don’t shy away from discussion of the prisoners’ crimes. But the tearful confessions, meant to stir our sympathy, are mainly rationalizations. One killer blames guns and fellow criminals; another blames his family for not being more talkative.

All of them find a message of redemption in “The Tempest,” which is touching, but what do we make of this? One actor/murderer is hit hard when he is denied parole after 12 years inside, and some will shed a tear along with him. But is 12 years an adequate sentence for murder? Those who would cheer lustily at a 20-year sentence for Ken Lay should think carefully.

We’d all like to believe that art is a lot more powerful than it is, but during rehearsals, two inmates who swear that Shakespeare has shown them the light are instead cast off to the Hole for breaking prison rules. An inmate in a previous production was granted parole but asked to stay for two more months because he had never finished anything in his life before. He did the play with pride. He was released. Then he committed suicide.

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SHAKESPEARE BEHIND BARS

[** 1/2] (Two and one-half stars)

The longest Bard.

Running time: 93 minutes.Not rated (profanity). At the Quad, 13th Street, between Fifth and Sixth avenues.