Under Atkins v. Virginia, 536 U.S. 304 (2002), it is unconstitutional to impose the death penalty on a mentally retarded defendant.

Tests of Johnson's IQ had led to varying results, as high as 83 (70-80 is borderline mentally retarded) and as low as 63 (mild mental retardation). The state Supreme Court held that reasonable minds could differ as to whether Johnson was mentally retarded, and remanded the case for a hearing.

The court relied heavily on evidence that Johnson had "defective adaptive skills, such as communication, self-care, social life, social and interpersonal development, self direction, and use of community resources." 102 S.W. 2d at 541. He "had deficient self-care skills in that he could not live alone and never had" and "had poor awareness of social mores." 102 S.W. 2d at 538-39.

Another expert apparently concluded that Johnson suffered from FAS. 102 S.W. 2d at 539. [Johnson's behavioral problems seem to be classic secondary disabilities of FAS.]

In relying on deficient adaptive skills as important evidence of mental retardation, the Missouri Supreme Court relied heavily on the Missouri statute which defined mental retardation. 102 S.W. 2d at 540. However, footnote 3 in the Supreme Court decision in Atkins defines mental retardation in similar terms.

[This decision may be significant in capital punishment litigation. The application of Atkins apparently is not limited to defendants whose cases were on direct appeal, or whose trials were after, the date Atkins was decided. Individuals with FAS typically function at a level lower than others with the same IQ. Thus in evaluating whether Atkins precludes execution of a particular defendant, it will often be important to determine if the defendant has FAS.]