The justices voted 6-3 Monday to reverse the 9th U.S. Circuit Court of Appeals' ruling in favor of Shirley Ree Smith. The appeals court had three times set aside Smith's conviction, saying the case likely was "a miscarriage of justice." The appeals court said there was "no demonstrable support" for the prosecution's theory of the case.
But the high court said that even though doubts about Smith's guilt are "understandable," the appeals court should have deferred to state courts that upheld the conviction of the Los Angeles-area woman.
Justices Stephen Breyer, Ruth Bader Ginsburg and Sonia Sotomayor dissented.
Ginsburg, writing for the dissenters, said the court should have passed up the chance to "teach the 9th Circuit a lesson" in a tragic case.
"What is now known about shaken baby syndrome casts grave doubt on the charge leveled against Smith; and uncontradicted evidence shows that she poses no danger whatever to her family or anyone else in society," Ginsburg said.
Smith was convicted in December 1997 and was sentenced to 15 years to life in prison.
After California appeals courts ruled against Smith, the federal appeals court first overturned the conviction in 2006. The judges rejected the prosecution's theory of the case, which included the assertion that Smith lost her temper when Etzel Dean Glass III began to cry and shook him to death at their home in Van Nuys, Calif.
Monday's unsigned majority opinion chided the appeals court for persisting in its views despite two earlier Supreme Court orders to review the case.
"It is not the job of this court, and was not that of the 9th Circuit, to decide whether the state's theory was correct. The jury decided that question, and its decision is supported by the record," the court said.