"Execution of Justice" is a deeply disturbing play, although not for the reason that may spring to mind if you are at all familiar with its subject matter: the Dan White murder trial.

White is the former San Francisco supervisor and ex-cop who shattered his star-spangled image forever in 1978, when he assassinated the city's mayor, George Moscone, and fellow supervisor Harvey Milk, the nation's first openly gay elected politician. After a divisive and inflammatory trial, White was convicted of two counts of involuntary manslaughter and sentenced to seven years and eight months. It was the lightest possible punishment (eventually reduced for good behavior) for what many believed, and still believe, was cold-blooded murder.

Using the words of the actual participants and transcripts from the courtroom, playwright Emily Mann has fashioned a sweeping drama about the trial, the events leading up to it and its awful aftermath. But if you expect to be unsettled by a blatant miscarriage of justice as you slip into your seat at Arena Stage, you are wrong. Or rather, you are only partially right.

What is extraordinary about this work, which opened last night in a stunning multimedia staging by Douglas C. Wager, is that it doesn't take one side over another. It takes all the sides and forces you to do as much. Just when you believe you've got your feelings in hand and your thoughts sorted out, Mann suddenly introduces an angry voice from the streets, a cry from the heart, a plea of utter bewilderment, and all your certainties are swept right out from under you.

Courtroom dramas do not usually operate in this fashion. While they may have some surprises up their somber black robes, by the evening's end they have revealed them all, made order out of disorder and brought the deadly motive to light. Mann's play is open-ended. It will leave you with worrisome questions -- not about White's guilt, perhaps, of which there is no doubt, but about a society that can produce such profound fissures. It will leave you with the question that White asked himself in his confession, tape-recorded only 90 minutes after the murders: "Why do people do things?" It will leave you, in fact, with a violent mixture of emotions: pity, indignation, befuddlement and sorrow.

Although White's trial provides the spine of "Execution of Justice," the play has the form of a huge dream. It jumps back and forth in time, juxtaposes courtroom testimony and anguished reactions from the community at large, and sometimes allows the defense and the prosecution to unfold simultaneously. "You have to understand," argues a desperate black lesbian leader (Kim Staunton), "that the Dan White verdict did not happen in a vacuum." Indeed, Mann fills that vacuum with dozens of voices, all screaming for relief.

We hear all the official witnesses. But we also hear what Mann terms "the uncalled witnesses" -- those on the fringes whose lives were implicated one way or another by Dan White's actions. A policeman, wearing a 'Free Dan White' T-shirt, expresses his disgust at the sexual depravity he encounters on his daily beat; a young gay man decries "the tyranny of the all-American boy"; a housewife, hearing the verdict over the radio, can only wonder, panic in her eyes, "What are we teaching our sons?"

Frequently as the testimony is unfolding, newsreel footage of the people and incidents in question are unreeling on a four-sided screen above the stage. The media, after all, were players in the trial, and the images they relayed to the world fanned passions already dangerously overheated. Wager doesn't leave it at that, however. He has set up his own TV cameras at Arena; the actors in the bright red square that serves as the witness stand are further exposed in wrenching close-up.

Just as Mann, eschewing easy partisanship, refuses to settle on one point of view, Wager won't let us take a single visual perspective on matters. A spotlight, for example, picks out Milk's friend (John Leonard), who remembers the candlelit march that poured down from the Castro district to the steps of City Hall the night of the murders. As he talks, hauntingly beautiful images of the vigil (from the documentary film "The Times of Harvey Milk") shimmer on the screen. At the same time, the Arena cast members, each carrying candles, are collecting onstage for a vigil of their own. The production is layered throughout with similar double and triple exposures. The mind is troubled even as the eye is torn.

And pain is everywhere. You see it in the brave countenance of White's wife (Gina Franz), struggling to maintain her composure in the courtroom. You hear it damming up the words, as a near-inarticulate White (Casey Biggs) confesses his crime to police officers who were once his buddies. You can see it wracking the body of Cyr Copertini (Tana Hicken), Moscone's secretary, as she recalls for the jurors the day White made his fateful office call, a .38-caliber pistol in his pocket. And you can't discount any of it.

It is rare that an American playwright tackles current events, which have pretty much become fodder for television docudramas of dubious merit. For that alone, "Execution of Justice" is exhilarating. It is theater reasserting its claim on the country's moral conscience. Rarer still, I think, is Mann's refusal to tidy up her subject for drama's sake.

That said, her documentary form carries certain limitations. The sprawl can be frustrating. Few of the actual participants in the case were possessed of verbal eloquence, and "Execution of Justice," relying on their words as it does, can't always escape the inchoateness of their emotions. The dialogue is like a chart of human confusion, not a road map to truth. Some spectators, I suspect, will want the truth distilled for them.

With 44 roles to fill, many of the actors must portray multiple characters, and that contributes another kind of confusion to the evening. We really shouldn't have to ask ourselves who's who, but now and then we do. What galvanizes this welter of material, however, is the urgency, bordering on zeal, that has seized the Arena cast. Biggs' intensity even in stillness is so riveting that when he does crack open, his confession is overwhelmingly powerful. Tom Hewitt, pursing Tallulah-red lips, as Sister Boom Boom, a transvestite "nun" and San Francisco street fixture, turns a plea for tolerance into a subtle call to violence, while Stanley Anderson plays White's defense attorney with slippery, manipulative skill. As White's aide, Sarah Marshall has only a few lines, but she invests them with bristling anger. Her performance is characteristic of the ensemble: Everyone seems to have a fiercely personal stake in what is going on.

Mann is certainly not about to let Dan White off the hook, but she won't let us off the hook, either. "Execution of Justice" puts nothing to rest. Stirring the ashes of the past, it uncovers a bed of coals that never went out. Execution of Justice, by Emily Mann. Directed by Douglas C. Wager. Set, Ming Cho Lee; lighting, Allen Lee Hughes; costumes, Marjorie Slaiman; technical director, David M. Glenn. With Casey Biggs, Gina Franz, Gregory Procaccino, Tom Hewitt, Ralph Cosham, Mark Hammer, Stanley Anderson, Tana Hicken, Henry Strozier, John Leonard, Kim Staunton, Cary Anne Spear, Terrence Currier. At Arena Stage through June 16.