The ruling came along the court's ideological axis.
The Orleans Parish (La.) District Attorney's Office conceded that it withheld a crime lab report favorable to John Thompson as it prosecuted him for attempted armed robbery. Withholding information favorable to the defense are called "Brady" violations under Supreme Court precedent in Brady vs. Maryland.
Because he was convicted, court records say, Thompson chose not to testify at a later murder trial, where he was convicted as well.
A month before his scheduled execution, prosecutors discovered the withheld lab report, and an appeals court threw out both of Thompson's convictions. In a retrial, Thompson was found not guilty of the murder charge.
Thompson then filed suit under federal civil rights law. A federal judge ruled that Thompson did not have to show a pattern of indifference of Brady violations when he could show that prosecutors were inadequately trained, and a jury awarded Thompson damages. The verdict was upheld by a divided appeals court.
But a narrow Supreme Court majority led by Justice Clarence Thomas ruled that a district attorney's office may not be held liable under civil rights law for failing to train its prosecutors based on only one Brady violation.
A plaintiff has to show some government action or decisions to prevail in such a suit, the majority said.