While I agree a pardon may be more appropriate, I suspect there is something you may have learned recently and you believe the new evidence will exonerate you, so you should find a lawyer with whom you may have a confidential consultation about this.
No sorry its too late to reopen the case. If you have not been in any trouble since you can apply for a pardon. A pardon would forgive the crime and restore all of your civil rights, like the right to vote and serve on a jury.
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