There is evidence. There is a confession. There is someone dead.
Unless the sentence was illegal, the only one likely to be able to change it is the judge who made it. Your fiance needs to talk with an Appellate Criminal Defense Lawyer in NC fast. The time to change such a sentence expires. If he's been in for 12 years, the time may have already passed.
Confidential information should not be disclosed in this Internet forum. This answer is not legal advice, which requires a personal connection and far more facts. This attorney does not give legal advice over the Internet. This is a general statement about law, not advice.
Sorry to say that there is plenty of evidence to convict. Convictions on false confessions are surprisingly common. Because he pled guilty, he gave up a lot of his appellate rights. Had he gone to trial, he would've preserved those rights. North Carolina has an actual innocence commission (google it) and that may be his best option. It's unlikely for a Motion for Appropriate Relief to be successfull unless there was prosecutorial misconduct or his representation was so inept that he has an Ineffective Assistance of Counsel claim.
There is also no formal way to change the sentence from box car to concurrent.
<a href="http://www.chetson.com">Raleigh criminal lawyer</a> Damon Chetson represents people in Raleigh, Cary, Apex, and the rest of Wake County, North Carolina. The information provided here is for educational purposes only and should not be relied upon as the specific facts may change the potential advice. Consult with a licensed <a href="http://www.chetson.net">Raleigh criminal lawyer</a> or attorney in your jurisdiction about your legal question or problem. For a free consultation about a North Carolina case, call (919) 352-9411 day or night, any day of the week.