The man accused of using Craigslist to lure a Twin Cities woman to his house and then killing her can't use his subsequent diagnosis of Asperger's disorder in his defense at his trial this month, a judge ruled Friday.

Defense attorneys contend that the disorder, a mild form of autism sometimes characterized by clumsiness and eccentric speech and behavior, explains how Michael John Anderson could have unintentionally shot Katherine Olson in his home in Savage in October 2007.

But District Judge Mary Theisen ruled that the defense's argument was insufficient to show that the Aspergers disorder diagnosed by defense psychiatrists had anything to do with the death. Further, she said, such testimony might invite jurors to speculate that he had diminished mental capacity or responsibility, a defense "not recognized in Minnesota."

Police say Anderson, 20, lured Olson, 24, to his house by posing on Craigslist as a woman needing a baby sitter. He allegedly shot her in the back before hiding her body in the trunk of her car, which was found in a Burnsville park. His trial on murder charges is set to begin in Scott County with jury selection next week.

Lead defense attorney Alan Margoles has acknowledged that Anderson was holding the gun, but he said his client didn't intend to kill Olson.

Anderson's statements to police allegedly included, "I thought it would be funny," and "I didn't kill her; the bullet did." Margoles argued in a pretrial hearing that the disorder played a key role in the shooting and his behavior afterwards.

Scott County prosecutors argued that the claim amounted to a diminished capacity defense. Under Minnesota law, determinations about diminished mental state must be made post-conviction.

Margoles countered that those with Asperger's aren't diminished but think differently. He compared his client to Mr. Spock of "Star Trek."

In her ruling, Theisen pointed out that Anderson hadn't previously been diagnosed with Asperger's or any mental illness.

Opening arguments are expected to begin March 23.

Abby Simons • 612-673-4921