The modern American death penalty has few advocates as aggressive and outspoken as Dale Cox. He is the acting district attorney of Caddo Parish, La., a poor region in one of the nation’s poorest states. From 2010 to 2014, prosecutors in Caddo Parish won more death sentences per capita than anywhere else in the country.

In March Mr. Cox drew national news coverage for his response to a former colleague’s public apology for putting a man on death row who later turned out to be innocent. “I think we need to kill more people,” Mr. Cox said.

The purpose of the death penalty, he has said repeatedly, is not to deter crime but to exact revenge. “Retribution is a valid societal interest,” he told The New York Times.

He has denied that the death penalty is racist or arbitrary, even though Caddo Parish, like most places in the country, applies it disproportionately in cases involving black defendants.