The justices said the appeal court should reconsider the case of Gary Donald Johnston in light of a 2014 Supreme Court decision about stings in which undercover investigators involve suspects in phoney crimes.
Johnston was seeking leave to appeal his case to the Supreme Court, but the justices instead referred it back to the lower court.
Johnston was sentenced to life with no parole eligibility for 17 years after he was found guilty in 2011 of killing a man who surprised him during a 1998 break-in.
He was only charged years after the crime when undercover police pretending to be major criminals managed to elicit an admission to the killing.
The Supreme Court last year ruled that judges must be leery of Mr. Big operations, although it didn't bar them completely.
The Supreme Court gave no written reasons for its decision to send the Johnston case back to the court of appeal, except for citing its earlier Mr. Big ruling.