The justices threw out a decision by the San Francisco-based 9th U.S. Circuit Court of Appeals in the case of Michael Robert Pulido, who was convicted for his role in robbing a gas station and killing the defendant.
A U.S. District Court judge set aside Pulido's conviction because the trial judge in the case gave the jury improper instructions.
The high court said in an unsigned opinion that the appeals court ruling affirming the federal judge's action used faulty reasoning. The justices did not reinstate Pulido's conviction.
Justices John Paul Stevens, Ruth Bader Ginsburg and David Souter agreed that the appeals court made a mistake, but would have affirmed its ruling anyway because the underlying decision in favor of Pulido was correct.
Last month, the court overruled the 9th Circuit in an environmental case involving the Navy's use of sonar and its potential harm to whales.
The case is Hedgpeth v. Pulido, 07-544.