NPR's Legal Affairs Correspondent Nina Totenberg reports on one of the issues being argued before the Supreme Court today: whether states should be forbidden to execute mentally retarded criminals. In recent years, states have been enacting laws against such executions, and the justices are thought to be considering a change in their 1989 position upholding execution of the retarded. In today's case from Virginia, a man and his accomplice kidnapped a third man, robbed and killed him. The defense says the man's history shows he is retarded. The state maintains he knew what he was doing and should be held accountable.