William Morva. (Matt Gentry/Associated Press)

ON JULY 6, Virginia is scheduled to carry out its third execution under Gov. Terry McAuliffe (D) and 113th since 1976. The inmate, William C. Morva, was convicted of fatally shooting two men — a deputy sheriff and a hospital security guard — in 2006. His guilt is not in question. What is less clear is if jurors would have sentenced him to death had they been aware of the true extent of his mental illness.

At varying points, Mr. Morva reportedly believed that he was meant to lead a distant indigenous tribe; that he was gifted with special powers to carry out an unidentified quest; that he was unjustly persecuted by local officials and the administration of President George W. Bush; and that his real name was Nemo, which is Latin for “nobody.” These are not signs of a rational mind, but rather one afflicted with debilitating mental illness. A mental-health expert who assessed him after his conviction diagnosed him with delusional disorder, a serious psychotic condition similar to schizophrenia.

We have previously written that capital punishment is dehumanizing. But the execution of a man suffering from severe mental illness is an act of particular barbarism — especially if his condition may have been misdiagnosed in trial. According to Mr. Morva’s attorneys, the mental-health experts who provided statements to the jury did not receive his full case history and diagnosed him with a personality disorder rather than psychosis.

Despite his personal opposition to the death penalty, Mr. McAuliffe is committed to upholding Virginia law, a stance we understand and respect. He commuted a death sentence in April, however, after he found flaws in the sentencing process of Ivar Teleguz. His predecessors — then-Gov. James S. Gilmore III (R) and now- Sen. Tim Kaine (D-Va.) — had granted clemency on grounds of mental illness. Mr. Morva’s case raises many of the same questions and adds fodder to the national effort to abolish capital punishment for people with serious mental illnesses.

Mr. McAuliffe should look favorably on the petition for clemency before him and commute Mr. Morva’s sentence to life in prison without the possibility of parole. He should also ensure that Mr. Morva receives the mental-health treatment he so obviously needs. The killing of two devoted public servants is a tragedy, but the state of Virginia will not right this wrong by getting more blood on its hands.