A U.S. Justice Department review has identified at least 175 federal prisoners who must be released or resentenced because they have been locked up improperly.

The review, which followed a USA TODAY investigation, found that some of those prisoners shouldn't have been imprisoned because they hadn't committed a federal crime. Others received sentences vastly longer than the law allows.

The problems stem from a misunderstanding about which North Carolina state convictions were serious enough to outlaw gun possession or require extended prison sentences under federal law. The number of prisoners ultimately freed or given shorter sentences is likely to be higher than 175 because the examination by federal prosecutors was confined to the smallest of North Carolina's three U.S. court districts. Justice Department spokesman Wyn Hornbuckle said "many more" cases could be upended when all are reviewed.