VANCOUVER - A B.C. man convicted of murdering a runaway teen has won his appeal and been ordered to stand trial again, only weeks after his father was convicted and sentenced for participating in the same crime.

B.C. Court of Appeal Justice Elizabeth Bennett said in a ruling posted online Wednesday that Justice William Grist erred because he did not give the jury instructions under some complicated evidentiary rules during the trial of Dustin Blue Robert Moir.

Moir was convicted Feb. 16, 2010 of first-degree murder for his part in the death of 14-year-old Chelsey Acorn in late 2005.

Bennett said a judge must provide instructions to a jury when a witness makes a statement in court that's inconsistent with a statement he or she has made previously, but those instructions were not given and that was an error in law.

"In my view there is merit to the appeal," said Bennett. "I would allow the appeal, set aside the conviction and direct a new trial."

Bennett also said Grist erred by admitting rebuttal evidence from the Crown and in his instructions to the jury regarding the motive for the crime, although she did not cite these reasons as grounds for a new trial.

Earlier this month, Moir's father, Jesse Blue West, was convicted of first-degree murder for participating in the crime and was sentenced to life in prison with no chance of parole for 25 years.

"The Crown's going to be carefully reviewing the decision before we make any determination as to what the next step will be in the case," said Neil MacKenzie, a spokesman for the Ministry of Attorney General's Criminal Justice Branch.

Acorn's remains were found "in a shallow grave" at the Carolina Mines campsite off the Coquihalla Highway in April 2006.

Bennett's ruling notes the side of her head was caved in and a large boulder was found nearby.

Available to jurors were two versions of events leading up to the murder, said Bennett.

In one version, Moir was an active participant or aid in the murder, but in the other he was a "fearful bystander and accessory after-the-fact," she said.

According to the version in which Moir was a participant and aid — a version obtained during a so-called Mr. Big operation by police — Moir and West had sex with the girl on the way to the campground.

Under that version of events, the campers set up a tent before Moir and West dug a grave.

"They entered the tent and bound Chelsey with duct tape," Bennett's said. "Mr. West then choked Chelsey. Mr. Moir said that she survived, and he completed the killing by choking her further."

Moir carried her body to the grave and then threw rocks on top of her, Bennett wrote.

Bennett noted that during the trial, Moir agreed with much of the evidence obtained under the Mr. Big operation, but testified he didn't know his father was going to kill the girl and he did not participate directly.

"His story was that he watched his father choke her in the tent and then, at his father's discretion, carried the body to the grave," said Bennett.

"The two then buried her, dumped her personal belongings and went to Mr. West's home."

A new trial has yet to be set for Moir for his role in the killing of Acorn, a girl who led a troubled life in the years leading up to her death.

According to Bennett's ruling, the Ministry of Children and Family Development took legal guardianship and permanent custody of the girl from her mother in April 2005.

But between March 2004 and June 2005, Acorn was placed in foster homes 18 different times, running away from her last home June 10, 2005.

Acorn was seen by a friend for the last time Oct. 23, 2005 in an Abbotsford, B.C. mall.

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