A week into the first-degree-murder trial of Bryan Lamar Lee, it ended in a mistrial Tuesday after a key witness for the prosecution abruptly changed his testimony.

Prosecution witness Tyler Brown was expected to testify that he helped Lee and another man dispose of Jordan “J.P.” Peterson’s body and that the other man — but not Lee — had admitted committing the murder to him.

Pima County Superior Court Judge Javier Chon-Lopez declared the mistrial after learning Brown had changed his story to indicate Lee had also confessed to participating the killing. Chon-Lopez agreed with Lee’s attorney that the new evidence to potentially come from Brown’s testimony would have come too late in the trial for Lee’s attorneys to adequately prepare for.

Lee, 22, was on trial for first-degree murder, aggravated robbery and kidnapping in the death of Peterson, whose decomposed body was found in the desert of Pinal County north of Marana in January 2012.

Brown’s attorney, Thomas S. Hartzell, told the judge on Tuesday his client asked to speak with him about his scheduled testimony.

“He told me he had been truthful but incomplete,” Hartzell said.

Brown had admitted to helping bury Peterson’s body. While he said the other man involved, Reed Marrone, admitted to killing Peterson, he said never said Lee made similar admissions until Tuesday.

Brown had previously agreed to testify for the state as part of plea deal in which he admitted to attempted concealment of a dead body.

Although testifying for the state, his testimony may have helped Lee, as he was expected to say he didn’t know if the defendant helped kill Peterson.

“Tyler Brown is a crucial witness,” defense attorney Joel Feinman said in arguing for a mistrial. “This considerably changes the entire nature of the case.”

Marrone, 20, pleaded guilty to first-degree murder and is serving 25 years to life in prison.

Contact reporter Patrick McNamara at 573-4241 or pmcnamara@azstarnet.com. On Twitter @pm929.