McKinney is on trial for robbery, kidnapping and murder in the death of the gay college student. His lawyers are seeking conviction on a lesser offense like manslaughter to avoid a possible death sentence.

They have two approaches, both of which are aimed at proving that McKinney suffered from a mental disease or defect that prevented him from knowingly or purposefully committing murder -- the ``diminished capacity'' defense.

When McKinney's defense gets into full swing Monday, the lawyers plan to offer testimony that his mental capacity was diminished by drugs and alcohol, an approach that is allowed under Wyoming law.

But they have combined that approach with the theory that a person with latent homosexual tendencies will have an uncontrollable, violent reaction when propositioned by a homosexual. Some have called this the ``gay panic'' defense.

McKinney's lawyers have contended he lost control during a drunken, drug-induced rage because a sexual advance by Shepard triggered memories of a childhood homosexual assault.

``It's the `excuse defense,' and it has never been allowed under Wyoming law,'' said Carbon County Attorney Tom Campbell, who is not involved in the prosecution of the case.

No state legislature has recognized the gay panic defense because there is no scientific evidence to support it, he said.

Judge Barton Voigt is expected to rule Monday on whether McKinney's lawyers will be allowed to present evidence supporting the theory.

McKinney and Russell Henderson, both 22-year-old roofers, are accused of luring Shepard out of a Laramie bar and taking him to a remote area near town, where they robbed him of $20, lashed him to a wooden fence and pistol-whipped him into a coma.

Shepard, 21, died five days later.

Henderson is serving two life sentences after pleading guilty to murder and kidnapping.

During testimony last week, prosecutors offered jurors a timeline of the events the night Shepard was beaten, ending with McKinney's jailhouse confession.

McKinney's then-girlfriend, Kristen Price, testified that he went on drug-and-alcohol binges that sometimes lasted for days. But she said she did not see McKinney use drugs or drink the day of Shepard's beating.

In his taped confession, McKinney said Shepard reached down and grabbed his leg while he was driving. He said he became angry and struck Shepard with his hands and a gun.

Diminished capacity defenses have taken unusual forms, none more notorious that the ``Twinkie'' defense used to help Dan White avoid a murder conviction for shooting San Francisco Mayor George Moscone and city supervisor Harvey Milk in 1978.

White, a former police officer and firefighter, contended his mental capacity was diminished from eating too much junk food.

In the furor that erupted over the verdict, the California Legislature abolished the diminished capacity defense. In 1985, White committed suicide months after he was released on parole.