Last week the state of Oklahoma killed SEAN SELLERS. He was the first person in 40 years executed for a crime committed at age 16, and the 10th juvenile offender executed in the U.S. this decade, more than in Saudi Arabia, Nigeria, Pakistan and Iran--the only other countries that are known to execute child offenders--combined.
Not only was he a child offender; Sean also suffered from a mental disorder. He was tried for three murders that took place in 1985 and '86: his mother Vonda, his stepfather Paul Bellofatto and Robert Bower. At trial, the jury was unaware that he suffered...