Washington (CNN) -- The Supreme Court issued a final, stinging rebuke of a lower court's decision on three separate occasions to dismiss the assault conviction of a grandmother in the shaking death of her 7-week-old grandson.
The justices in an unsigned opinion Monday said the 9th Circuit U.S. Court of Appeals "plainly erred in concluding the jury's verdict was irrational." The high court for the last time reinstated the conviction of Shirley Ree Smith, ending a 15-year legal fight.
Prosecutors alleged Smith lost her temper and violently shook Etzel Dean Glass III when he woke up crying and in need of a diaper change in Van Nuys, California, in 1996. The boy's mother had put him to sleep on a sofa, and the grandmother was sleeping on the floor next to Etzel.
An initial diagnosis of sudden infant death syndrome (SIDS) was changed to shaken baby syndrome (SBS) after an autopsy. That conclusion formed the basis of the government's case, but was strongly challenged by the defense. A jury convicted her, and Smith, then 37, was sentenced to 15 years to life.
After subsequently losing in state courts, Smith's lawyers asked for a federal appellate review. The San Francisco-based 9th Circuit overturned the conviction, saying her case was probably a "miscarriage of justice."
In one opinion, the judges ruled government experts "reached [their] conclusion because there was no evidence in the brain itself of the cause of death."
That assessment, said the high court on Monday, "is simply false. There was evidence in the brain itself ... these affirmative indications of trauma formed the basis of the experts' opinion that Etzel died from shaking so severe that his brainstem tore."
A key government witness, Dr. David Chadwick of the San Diego Children's Hospital and Medical Center, testified the child suffered brain contusions that bled into his optic nerves, a result of a "violent shaking," and that death occurred quickly after the trauma began.
"Doubts about whether Smith is in fact guilty are understandable," said the justices. "But 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."
Justice Ruth Bader Ginsburg criticized the majority for "its misuse of discretion" by agreeing to take the case, then summarily disposing of Smith's appeal.
"I would not ignore Smith's plight and choose her case as a fit opportunity to teach the 9th Circuit a lesson," she said.
"What is now known about shaken baby syndrome (SBS) 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."
Added Ginsburg, "By taking up the case, one may ask, what does the court achieve other than to prolong Smith's suffering and her separation from her family. Is this Court's intervention really necessary? Our routine practice counsels no."
The court's oldest member was supported by Justices Stephen Breyer and Sonia Sotomayor.
Smith, who had been released from custody after the earlier appeals court victories, will now likely be returned to prison to serve the rest of her sentence.
The case is Cavazos v. Smith (10-1115).