In 1977, as part of its wide-ranging re-examination of capital punishment, the Supreme Court prohibited the death penalty for rape. While that ruling, Coker v. Georgia, did not specifically discuss the rape of a child  the victim, although only 16, was a married woman who was raped at knifepoint  the decision has been widely understood as limiting the death penalty to the crime of murder.

In the principal opinion in the Coker case, Justice Byron R. White wrote that “we have the abiding conviction that the death penalty, which is unique in its severity and irrevocability, is an excessive penalty for the rapist who, as such, does not take human life.”

But in recent years, a handful of states, responding to public outcries about sex crimes against children, have amended their death penalty statutes to make the rape of a child a capital offense. Louisiana was the first to do so, amending its death-penalty law in 1995 to apply to the rape of a child under the age of 12. The other states with similar provisions are Georgia, Montana, Oklahoma, South Carolina and Texas. Unlike Louisiana, most limit the death penalty to defendants who were previously convicted of sexual assault against a child.

The Louisiana Supreme Court rejected Mr. Kennedy’s appeal last year in a 64-page opinion that concluded that “rape of a child under the age of 12 years of age is like no other crime” and that death was not a disproportionate punishment. Taking note of the recent state laws, the court said there was “compelling” evidence of a national trend toward treating the crime as distinct from others.

The United States Supreme Court’s recent death penalty jurisprudence has paid close attention to evidence of whether contemporary society has reached a consensus on particular applications of capital punishment. The court relied on such an analysis to rule out the death penalty for mentally retarded defendants in 2002 and for juvenile killers in 2005. Louisiana is now invoking the same approach to argue that an application of the death penalty once widely deemed unconstitutional has become permissible.