An 18-year-old Big Water man pleaded guilty Monday in a plea agreement to murdering his 6-year-old cousin.

The agreement allows defense attorneys to continue to challenge James Bybee's confession.Bybee's plea came on the day he was to go to trial before 6th District Judge K.L. McIff for the slaying of Lance Guevarra, and just two weeks after the Utah Supreme Court decided his confession to Kane County Sheriff's Deputy Allen Johnson wad admissible as evidence.

McIff will sentence Bybee on May 15 for the first-degree felony, which carries a possible prison term of five years to life. Meantime, Bybee's lawyers will weigh their options in taking the state high court's ruling to the U.S. Supreme Court.

Prosecutors agreed to accept the plea with that condition.

"I'm happy to have this portion behind us," said Kane County Attorney Colin Winchester.

Guevarra disappeared without a trace from the small, mostly polygamous community of Big Water on Aug. 14, 1996. Lawmen were baffled by the disappearance.

In February 1997, Bybee - in a Las Vegas mental institution following a suicide attempt - confessed to police and led them to a shallow grave less than a quarter-mile from the trailer where the boy was last seen.

Bybee, who was related to Lance by a polygamist marriage, was the last person to see the boy alive the night he disappeared. The boy, clutching two Godzilla dolls, left the cousin's trailer home to go back to his own trailer 50 feet away to get a Nintendo video-game cartridge.

Lance's father, William Guevarra, has three wives and Bybee is the nephew to one of them.

Defense lawyers are concerned over the circumstances surrounding Bybee's confession. Bybee, who was 16 at the time of the killing, repeatedly asked to have his father present when Johnson interviewed him, but Johnson refused.

Defense lawyers maintain Bybee's request amounted to a request for counsel, which would have required Johnson to cease the interview immediately.

But McIff declared Johnson's interview proper, and, on March 20, the Utah Supreme Court upheld the judge's ruling.

At the time of the boy's disappearance, Bybee was staying at his mother's home, next door to the Guevarra's trailer. He later lived with his father in Las Vegas, where he was hospitalized after attempting suicide Jan. 7, 1997.

When Bybee began talking about Lance, his doctor was obliged to go to the police because of a Nevada law requiring health-care providers to report suspected child abuse, said Winchester.

At Guevarra's preliminary hearing in July, Johnson testified that Bybee told him he killed the young boy to punish William Guevarra.

"He said that all his life he had lived next to the Guevarras and that Will (the father) would brow-beat him. He said that he wanted to get back at Will," Johnson said.