State District Judge Barton Voigt told lawyers for Aaron McKinney that the strategy was, in effect, a temporary insanity or a diminished capacity defense, both of which are prohibited under Wyoming law.

McKinney, 22, is charged with first-degree murder, kidnapping and aggravated robbery in Shepard's death last year. The 21-year-old University of Wyoming political science major suffered at least 18 blows to the head.

Prosecutors say McKinney and Russell Henderson, 22, posed as homosexuals, lured Shepard out of a downtown bar, drove him to a remote fence, tied him to it and pistol-whipped him into a coma. Police said robbery was the main motive but that Shepard may also have been singled out because he was gay.

During opening statements, the defense told jurors that the crime was triggered by a combination of McKinney's drug and alcohol use, traumatic youthful homosexual episodes and an unwanted sexual advance by Shepard.

They had hope to borrow a page from what is informally called a ``gay panic'' defense, built on a theory that a person with latent gay tendencies will have an uncontrollable, violent reaction when propositioned by a homosexual.

Prosecutor Cal Rerucha countered that such testimony would give others an excuse to kill people they don't like, such as minorities.

And the judge said today that he did not believe defense attorneys had offered any evidence that such a strategy would be relevant.

``Even if relevant, the evidence will mislead and confuse the jury,'' he stated in a written order released before the trial resumed today.

McKinney could receive the death penalty if convicted. Henderson received two life sentences after pleading guilty in April to felony murder and kidnapping.

Lawyers for Aaron McKinney rested their case several hours later.

District Judge Barton Voigt ruled that the strategy adopted by McKinney's lawyers in the beating death of the gay college student is akin to temporary insanity or a diminished-capacity defense -- both of which are prohibited under Wyoming law.

``What the defendant is trying to do is to raise a mental status defense that is not recognized by Wyoming law, and of which there has been no notice and no opportunity for the court or opposing counsel to consider before trial,'' he said. ``Even if relevant, the evidence will mislead and confuse the jury.''

McKinney, 22, could get the death penalty if convicted of murdering Shepard, who was lashed to a fence and left to die on the prairie last year.

A ``gay panic'' or ``homosexual panic'' defense is built on the theory that a person with latent gay tendencies will have an uncontrollable, violent reaction when propositioned by a homosexual.

McKinney's lawyers have said McKinney flew into a drug-induced rage after a sexual advance by Shepard triggered memories of traumatic, youthful homosexual episodes.

The defense called seven witnesses, including two men who claimed Shepard made unwanted sexual advances toward them. Closing arguments are set for Tuesday.

The attorneys on both sides are prohibited from commenting by a judge's gag order.

Other lawyers noted that McKinney's attorneys still could argue that the crime happened in a moment of passion.

``This was gravy or frosting, but it certainly wasn't the whole shooting match,'' said Carbon County prosecutor Tom Campbell. ``They must have known ahead of time that their odds for getting that into evidence were slim and I don't think good lawyers rely on evidence that is slim.''

Prosecutors said McKinney and Russell Henderson, 22, posed as homosexuals, lured Shepard out of a bar, drove him to a remote fence and pistol-whipped him into a coma. Police said that robbery was the main motive but that Shepard may also have been singled out because he was gay. Henderson pleaded guilty in April and is serving two life sentences.

Some gay rights leaders have condemned the ``gay panic'' defense as a blame-the-victim strategy. However, Bill Dobbs, a gay New York lawyer and civil rights advocate, said the defense should be allowed wide latitude in death penalty cases.

``Gay panic exists and any gay man knows that just holding the gaze of a straight man on the street and giving him the idea that you might be sexually interested can create a dangerous situation,'' he said.

The decision came as McKinney's attorneys began presenting their first full day of testimony.

Among the witnesses who testified was McKinney's stepsister, Afton Timothy. She said that McKinney's girlfriend, Kristen Price, told her that Shepard ``reached over and grabbed Aaron's crotch'' and ``Aaron got mad and hit him in the truck.''

Dr. Robert Lantz, a toxicologist, testified that methamphetamine can cause violent outbursts, especially in chronic users.