A schizophrenic man has pleaded guilty to killing his brother, resolving a case that came before the Utah Supreme Court over the role of mental illness in murder prosecutions.

Eryk Drej, 37, accepted a plea bargain Wednesday, admitting that he killed his younger brother in June 2005. Lukasz Drej, 25, was shot 22 times while he was sitting in his truck talking on a cell phone outside their American Fork home.

Police say Eryk Drej believed his sibling was involved in a plot to kill a woman and sell her organs on the black market. A judge initially determined he was incompetent to stand trial, but he was found competent after seven months of treatment at the Utah State Hospital.

"This is a very unusual case. He was mentally ill at the time he committed the murder, but he didn't know he was mentally ill," said prosecutor Jeff Buhman. "Even his family had no idea what was going on."

According to Utah law, if Drej had been found guilty of first-degree felony murder, a jury could lower the conviction to second-degree felony manslaughter by considering the crime from the perspective of his delusion.

The statute, however, did not say whether the prosecution or defense has to prove that he was suffering from a delusion.

Drej's defense attorneys argued that placing the burden of proof on the defendant is unconstitutional. But in May, the Supreme Court disagreed, a decision that would have required Drej's defense attorneys to prove he was delusional in order to be convicted of manslaughter instead of murder.

Under Wednesday's plea bargain, Drej pleaded guilty to first-degree felony murder but will be sentenced as if the crime were a lesser second-degree felony — but he will get no credit for the five years he's already served.

Drej faces up to 15 years in prison when he is sentenced Oct. 20 in 4th District Court.