Like many others, I lost someone on 9/11, a young man happily married with a first child a week away from being born. I knew him when he was a teenager, my daughter's first love, my son's favorite friend to play catch with, a boy we took with us on vacations. He died a horrible death in the World Trade Center, an unasked-for death, unexpected and undeserved. He was killed by men we would call very bad indeed - but whom they, the bombers and their teachers, would call heroes, heroic actors on a world stage.

So how do we Westerners wrap our minds around the concept that some men decide to live only in order to kill themselves, and do it by taking as many other living creatures with them as possible? Is it the 72 virgins waiting for them in paradise? Not really, since they can look forward in real life to marrying at least one and perhaps four - and finding out that virginity is not all it's cracked up to be. Is it that life on earth is so horrendous, so filled with pain and suffering, that death is preferable? Millions of sub-Saharan Africans lead lives of incredible pain and poverty and hopelessness, and yet they try desperately to stay alive. Even the Jews in Auschwitz hoped to survive, and when they died they often tried to save the lives of others; Muslim suicide bombers lead ordinary lives of no more than ordinary pain and pleasure, and yet they live to kill. "You are in love with life," one of them famously said about the West. "We are in love with death."

The idea that one can regard oneself as just an instrument, a cipher, a dot in a larger canvas, someone else's property - without a persona or perspective or thought; the idea that one lives only in order to die, and in order to kill unknown numbers of others while doing it, regarding other humans as mere ciphers as well, violates every tenet I live by, and is beyond my ability to comprehend.

All these inchoate thoughts come, of course, upon the occasion of Paul Greengrass's film "United 93." I dreaded watching it because it describes the kind of tragedy that can never be resolved or cathartic; it cannot give us any kind of release. In a way, the film's own quality or lack of it would be immaterial, irrelevant, because the memories of the day can never be healed. They will be an open wound forever.

But my fears about the film were needless; it is fine, if that's not too bland a word. Written and directed by Paul Greengrass ("Bloody Sunday," "The Bourne Supremacy") and shot and edited with powerful verisimilitude, the film begins with four men praying in Arabic; they will board United 93 in order to hijack it and fly it into the U.S. Capitol.

Greengrass cuts back and forth from the passengers boarding the plane to the cockpit crew to the control centers. He lets us in on the workings of the air traffic controllers in the Boston, New York and, finally, the Cleveland center. It is a beautiful Monday, the usual little problems are under control. But slowly the unthinkable begins to take over everyone's life: a plane, then two, then three are departing from their flight paths and are not in contact anymore. Meanwhile, United 93 - the fourth to be hijacked - is delayed on the ground at Newark. When the first plane strikes the World Trade Center the controllers still cannot imagine that an airliner has been deliberately hijacked to do it. They are not stupid; they are us, you and me. As they realize what has happened, they take action - but they're hampered by the fact that neither the President nor the Vice President can be reached in this emergency. (If you saw Michael Moore's "Fahrenheit 9/11" you know where the President was.)

Working from what he learned from tapes and phone calls from passengers, and without a star or even a recognizable name in his cast, Greengrass takes us through the flight of United 93 - the attack on the cockpit and the presumed murder of the captain and copilot; the murders of passengers, and finally the rush to retake the plane. Crosscutting this with the controllers and the Air Defense Command - left without planes or orders to intercept - Greengrass builds his film through hand-held shots and quick cuts up to the final moment when he ends the film.

In two pieces of inspired casting, he has Ben Sliney, the head air controller, and Major James Fox, of the Air Defense sector, play themselves. They are so believable in their professionalism and honest confusion and ultimate courage that they make us cry whenever they are on screen. They let us see in to their dilemmas, their reactions, their decisions; they are magnificent.

"United 93" is more a life experience than a film, but as a film it is essential also. And how many films can we say that about?