On March 29, 1994, a story appearing in the Washington Post began as follows: INSANITY DEFENSE: NOT A RIGHT IN MONTANA CASE, JUSTICES GIVE STATES OPTION TO PROHIBIT CLAIM

The Supreme Court yesterday allowed states to prohibit defendants from claiming that they were insane at the time they committed their crime. The court, without comment from the justices, let stand a ruling from the Montana Supreme Court that said abolishing the insanity defense does not violate the Constitution. This sounds like an important story. But it wasn't. In fact, the Court's action was hardly newsworthy at all. The Justices simply denied certiorari. In other words, the Court decided not to hear the case. This is not a decision on the merits. The Court did not pass on the constitutionality of the Montana statute. In fact, the Court's decision has no precedential value, as even the Post article noted in the second paragraph of the story: While the Court's order does not apply beyond the individual case, other states could follow Montana's lead. Of course they could. They could have done so since 1979 when the statute was enacted. But only two more states (Idaho and Utah) did.

Citation
Richard J. Bonnie, Lorena Bobbitt: "Moral Mistakes" and the Price of Justice, 14 Developments in Mental Health Law 20–23 (1994).