There had been no physical evidence to support Smith's original murder conviction in 1997.
Instead, the jury chose to believe prosecution experts, who surmised that Etzel had been killed by shaking, over doctors testifying for the defence, who said it was a classic example of Sudden Infant Death Syndrome.
A decade into her sentence, Smith was freed on appeal. The US 9th Circuit Court of Appeals announced she had suffered a "miscarriage of justice". The evidence against her was so flimsy that there was "no demonstrable support" for the prosecution's version of events, it said.
Then came this week's decision. Reached by a 6-3 majority at the highest court in America, it revolves around a legal technicality: although the Supreme Court says doubts over Smith's guilt are "understandable", it also believes appeal judges have no right to decide a jury reached the wrong conclusion.
"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," read the Supreme Court verdict. "The jury decided that question."
Only fresh evidence, or evidence of misconduct at the original trial, can be used to overturn a conviction.
Smith's case is already a cause celebre among campaigners who say misguided expert witnesses have contributed to a slew of wrongful "shaken baby" convictions.
The three Supreme Court justices who supported Smith say it is unlikely, given recent research into the sudden death of infants, the prosecution witnesses would have testified so vigorously today.
"What is now known about shaken baby syndrome casts grave doubt on the charge levelled against Smith; and uncontradicted evidence shows that she poses no danger whatever," they wrote.
Smith's only chance of avoiding jail revolves around a clemency petition. But her lawyer, Michael Brennan, says the chances of it being granted are "extremely slim".
- Independent
