A writ or a pardon are his only options. And he has a much better chance at a writ. You would need to hire an appellate attorney to review the record for possible grounds for a writ.
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The only two ways to challenge a conviction are by direct appeal or by writ. You will need to hire a lawyer (a different one from his trial lawyer) to raise these issues.
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Your brother's only options as to getting his case overturned are by direct appeal or by writ. The direct appeal route may be foreclosed if a timely notice of appeal or motion for new trial was not filed. Your brother should seek counsel immediately.