When Theodore Kaczynski goes on trial Monday, he will do so amid virtually unanimous consensus — his defense team included — that he is the Unabomber, that he did in fact make and send bombs that killed two and injured two others.

The where, when and how of the case are already known, puzzles solved by the discovery of his squalid Montana cabin and the documents and devices found inside. All that remains is the why — why such a promising, brilliant mind became so twisted, why he chose to express his hatred of technology by destroying the lives of innocent strangers.

And as the trial unfolds, one more why will beg for an answer. Why did not the Justice Department accept a guilty plea and a sentence of life without parole, thus avoiding this sordid spectacle of madness and grief, ensuring that Kaczynski will not not become a death-penalty martyr, guaranteeing that he will never again cause harm.

The offer was on the table. Kaczynski would plead to all counts, he would spend the rest of his life behind bars. In return, Janet Reno’s Justice Department would not seek death during the penalty phase of the trial. But Justice rejected the deal, apparently preferring to bring the full weight of the U.S. government against a pathetic man who, whether he meets the strict legal definition or not, clearly is mentally ill.

It would not have been just the humane thing to do, it would have been the smart one as well. As far too many recent high-profile trials have shown, a lot can go wrong in what appears to be a prosecutorial slam-dunk. Although the defense cannot present expert testimony on mental illness, the jury certainly can infer. One sympathetic juror and it’s back to square one. Twelve and Kaczynski walks.

That’s highly unlikely, of course. Much more probable is that Kaczynski, at the government’s urging, will be sent to death row, where he will stay for years as the appeals drag on. And those appeals could bear fruit. It is well established that Kaczynski has not cooperated with his court-appointed attorneys. It would not be too great a leap for an appeals court to rule that he was not adequately represented.

If the appeals fail and Kaczinski does face the executioner years from now, he will go out in a blaze of candlelight vigils, with death-penalty opponents joined by those who believe it is wrong for a civilized society to kill its mentally defective members. Even the most vengence-minded cannot see such celebrity as preferrable to the anonymity of a life lived out in a cold and lonely prison cell.

In accepting the plea offer, the Justice Department would not have prevented a sentence of death, it merely would have made a recommendation. Relatives of the victims still could have testified as to their loss and to their desire for the ultimate penalty had they wished, and the jury could have imposed it.

Finally, there is the matter of trust. The government probably still would be looking for the Unabomber were it not for David Kaczynski. Noticing similarities between the published manifesto and his older brother’s beliefs, David Kaczinski stepped forward, hoping to stop the bombings, hoping to get help for his brother.

While not expressly promising to pass on the death penalty, the government clearly led David Kaczinski to believe it, too, was concerned about his brother’s mental state — a promise was implied. David Kaczinski did the right thing. He almost certainly saved lives. He should not have to bear the guilt of sending his brother to his death.