A federal magistrate judge in West Virginia on Monday recommended overturning the conviction of Donald L. Blankenship, a former coal executive who served one year in prison after a deadly 2010 explosion at his company’s mine, saying prosecutors withheld evidence that could have led to his acquittal.

Mr. Blankenship was convicted in 2015 of conspiring to violate federal mine safety standards, a misdemeanor, more than five years after the explosion ripped through the Upper Big Branch mine, about 30 miles south of Charleston, W.Va. Twenty-nine people were killed. He was not accused of direct responsibility for the accident, but the inquiry that led to his conviction was prompted by the disaster.

The conviction was upheld by the United States Court of Appeals for the Fourth Circuit, and the Supreme Court declined to take his case in 2017.

But on Monday, the federal magistrate judge, Omar J. Aboulhosn, said in a 60-page ruling that prosecutors should have turned over 61 memorandums of interviews conducted by federal agents and other documents that could have helped Mr. Blankenship mount a better defense.