An appeals court has rejected an attempt to overturn the most serious of the criminal convictions resulting from a mass shooting at Oxford High School in Michigan, according to court documents filed Tuesday.

The Michigan Court of Appeals denied Ethan Crumbley’s request to appeal his life sentence, citing a "lack of merit in the grounds presented."

A three-judge panel of the Michigan Court of Appeals denied the Oxford High School shooter's requests to withdraw his guilty plea or be resentenced.