The man was 17 when he was arrested following the death of Adam Cavanagh, who was shot in the head through a basement window of his northeast-area home in February 2007.
He was given a 10-year sentence, but his lawyer said the trial judge made a number of errors.
The case was brought before the Alberta Court of Appeal, where the defence argued for a new trial on a charge of second-degree murder.
The high court has now granted a retrial, but the panel says in a seven-page decision that it should be by indictment on the original charge.
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