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Tennessee plans to put Tony Carruthers to death on May 21. He would be the 17th execution in the Volunteer State in the last half-century.

The state killing of Carruthers would also be one of the most unjust executions ever carried out there or anywhere else where the death penalty is legal in the United States. Carruthers’ case is a perfect storm of capital punishment’s familiar failures: paid informants, information withheld from the jury, untested physical evidence, and the defendant’s mental illness.

Most egregiously, Carruthers was forced to be his own lawyer during his trial. If Carruthers is executed, he would be the first person in nearly a century to be executed after being forced to represent himself.

The courts should step in to stop such a miscarriage of justice. They should act quickly and grant the motion requesting DNA testing that was filed by the American Civil Liberties Union and the ACLU of Tennessee in the state Supreme Court earlier this month.

If judges will not step in, Tennessee Gov. Bill Lee should use his clemency power to spare Carruthers.

Carruthers, along with his co-defendant James Montgomery, was sentenced to death for the 1994 killings of Marcellos “Cello” Anderson, his mother Delois Anderson, and Frederick Tucker. To convict him, the state relied on the testimony of a paid jailhouse informant, while no physical evidence suggested he was present at the crime scene.

We know that the use of jailhouse informants is a leading cause of wrongful convictions in capital cases. Northwestern University’s Center for Wrongful Convictions says that what it calls the “Snitch System” accounts for “45.9% of........

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