Omar Khadr should be serving his time in a provincial facility and must be transferred from federal prison, the Alberta Court of Appeal ruled Tuesday.
Khadr, a Canadian who pleaded guilty in a U.S. military court to war-crimes charges, would have been sentenced as a youth had he been in Canada, the judges wrote.
Khadr was transferred to Canada under the International Transfer of Offenders Act.
"We conclude that Khadr ought to have been placed in a provincial correctional facility for adults," wrote Justices Catherine Fraser, Jack Watson and Myra Bielby.
"In summary, the eight-year sentence imposed on Khadr in the United States could only have been available as a youth sentence under Canadian law, and not an adult one, had the offences been committed in Canada."
Omar Khadr wins appeal, will be transferred from federal prison