The trial court found the defendant guilty and sentenced him to life imprisonment. The appellate courts affirmed and the case moved up to the U.S. Supreme Court. After barely two months' deliberation the high court also affirmed. Nothing in the concept of "due process," said Justice Souter, prevents Arizona from defining its insanity test narrowly. The state must demonstrate only that Clark was not afflicted with a mental disease "of such severity that he did not know his criminal act was wrong."

After 16 years on the high court, Souter remains a stylistic disappointment. Now and then -- rarely -- he gets off a sentence of remarkable clarity. Mostly he writes in paragraphs of impenetrable prose, festooned with a fungal clutter of unnecessary footnotes. He says:

"Though Clark is correct that the application of the moral incapacity test (telling right from wrong) does not necessarily require evaluation of a defendant's cognitive capacity to appreciate the nature and quality of the act charged against him, see Brief for Petitioner 46-47, his argument fails to recognize that cognitive incapacity is itself enough to demonstrate moral incapacity. Cognitive incapacity, in other words, is a sufficient condition for establishing a defense of insanity, albeit not a necessary one."

In the final paragraphs of his 39-page opinion, Souter abruptly lapses into lucidity. He quotes approvingly from authorities who doubt that psychiatrists and psychologists are "more qualified than any other person" to give an opinion on whether a defendant's mental condition adds up to insanity.

Justice Anthony Kennedy, joined by Justices Stevens and Ginsburg, filed a salty dissent. (Justice Breyer dissented separately.) He fumes that Souter has invented an unworkable theory to justify a verdict of insanity. Then the majority applied the theory unfairly by holding Clark's counsel responsible for not having divined Souter's novel approach.

The long and short of it is that Eric Clark has been found sane enough to serve 20 years in the slammer. If he ever was crazy, nobody proved it.