The Supreme Court on Wednesday probed deeply into what a state needs to do to allow defense lawyers for a client with mental problems to mount a defense to criminal charges, but left the impression it wants to act narrowly to avoid putting tight limits on a state’s options. In a case dealing both with the scope of the insanity defense itself and some lesser claim of diminished mental capacity,.the Court showed little inclination to compel a uniform definition of insanity, but appeared interested in fashioning a way to make sure the defense can meaningfully answer prosecutors’ evidence of criminal intent. The case was Clark v. Arizona, docket 05-5966. (Kimberly Morris’ excellent summary of the case can be found just below this post.)

The Court has never held that a state must allow an insanity defense, and it has left the states with leeway to decide how to define such a defense if one is allowed. Justice Antonin Scalia on Wednesday reminded everyone of those basic propositions, and the flow of the argument did not suggest that the Court was likely to alter them in the Clark case. Arizona uses a trumcated version of the traditional “McNaghten rule,” and the Justices did spend some time getting a better understanding of the implications of Arizona’s approach; there was no direct assault on it from the bench, however. Justices Stephen G. Breyer and Anthony M. Kennedy suggested, in fact, that the Arizona version may be sufficient to get at the insanity question.

But Arizona has gone further: in essence, it requires defendants to rely on the insanity defense even in its abbreviated form as their sole means of using mental capacity evidence to counter the prosecution on the crucial intent issue. The state does not permit a “diminished capacity” defense, as such, and, moreover, it does not allow “diminished capacity” evidence to be offered at all outside the insanity context. It is this combination against a mental defect claim that several members of the Court appeared to find troubling.

In Eric Michael Clark’s case, several Justices pointed out, the state specifically charged the accused with the intentional killing of a police officer, and thus that specific intent was a crucial issue. The prosecution sought to show that intent with evidence that Clark had told others he planned to kill police, and he took steps to lure police to a neighborhood so he could carry out his plan. The defense tried to counter that initially by a claim of insanity. But, when that failed, the defense tried unsuccessfully to get the judge to consider the claim that Clark could not be found to have intended that killing, because his mental state at the time had led him to believe he had killed an alien, or a Martian, not a policeman.

As the hearing moved along, the Justices’ fascination with that claim, and how it might have been put forth at the trial, appeared to deepen. The questions focused on what it might mean to the defense if it could show that Clark knew it was wrong to kill people, but did not know it was wrong to kill a Martian, and that is what he may have believed he had done. The clear implication was that, since it was not an explicit claim of insanity, whether it should have come into evidence, in some way.

A fine line of distinction, though, appeared to emerge: the Court might be inclined to make some room for this as a matter of evidence, but not as a full-scale diminished capacity defense. Justice David H. Souter suggested why the distinction: “Everyone charged with a crime would have an impaired capacity defense, and there would be no criminal law,” he said. That, he said, was what drives a state to deny such a defense. But Clark’s lawyer, David L. Goldberg of Phoenix, said that this factor would not be as compelling if the defense simply sought a chance to offer evidence of diminished capacity to counter a prosecution assertion of intent.

When the lawyer for Arizona, Randall M. Howe, appeared, Justice Kennedy wondered aloud whether trial judges in the state would be able to consider all of the evidence that might bear on intent, if mental capacity evidence could only come in on the question of insanity. Justice Ruth Bader Ginsburg appeared to echo that concern. And Chief Justice John G. Roberts, Jr., questioned whether there was something special about mental capacity evidence that led the state to ban it, outside the insanity context. Howe, who is chief counsel in the state attorney general’s office, said such evidence is too difficult for juries to sort out, because it requires them to draw “fine gradations” about mental capabilities.

Solicitor General Paul D. Clement made a brief appearance, focusing his argument mainly on the suggestion that Arizona has fashioned an insanity defense that it deems proper, and wants to protect the integrity of that defense by excluding evidence about mental capacity that would undermine its policy choice.