Chase Freed, who is 20, pleaded guilty on Monday to the second-degree murder of Jim Williams in Red Deer in December 2019.
RCMP said at the time that a masked man armed with a sawed-off semi-automatic rifle shot Williams, who was 69, in front of his wife in the store’s parking lot during an attempted robbery.
Williams died in hospital.
The plea came after jurors had been selected for a trial that was scheduled to last three weeks.
The sentencing hearing is set for two days.