The judges held that the presence of three features of "shaken baby syndrome" did not automatically lead to a conclusion of unlawful killing or injury.
The court allowed an appeal by Raymond Rock, of Great Yarmouth, Norfolk, against his conviction of murdering his girlfriend's daughter, Heidi Davis, aged 13 months, in 1998 and reduced the verdict to manslaughter.
He was alleged to have shaken the child violently, but he insisted she wriggled out of his arms and fell to the floor. He was still serving his sentence.
Lorraine Harris, 36, of Long Eaton, Derbyshire, who was jailed for the manslaughter of her four-month-old son, Patrick McGuire, in 2000, had her conviction quashed. She said the baby became ill and stopped breathing after a vaccination. He had a blood disorder that was discovered only after his death. She has been released from prison but was banned from seeing her other child.
Michael Faulder, 34, jailed for two-and-a-half years at Teesside Crown Court in 1999 for causing grievous bodily harm to a seven-week-old boy, was cleared. He argued that he accidentally dropped the baby. The child made a full recovery.
But the judges dismissed an appeal by Alan Cherry against his conviction at Birmingham Crown Court in 1995 of the manslaughter of his girlfriend's 22-month-old daughter, Sarah Eburne-Day. He denied shaking her in a fit of temper and claimed she fell off a stool. He was no longer in custody.
Rock, originally sentenced to life, was given a seven-year sentence for manslaughter. His solicitor, Campbell Malone, said that since he had served six years, he should be released.
Defence lawyers argued during a two-week Court of Appeal hearing last month that medical knowledge and opinion had changed over the years to the extent that the convictions could no longer be considered safe.
The jury in each original case was asked to infer from the expert evidence that the child victim had been violently mishandled by the defendant in a momentary loss of control or temper, said Michael Mansfield QC.
Yet there was no other evidence about what happened and no evidence of earlier ill-treatment. New research since 2001 had led to a reappraisal of the "triad" of features involved in shaken baby syndrome - more accurately, non-accidental head injury (NAHI) - which are swelling of the brain, bleeding between the brain and the skull, and bleeding in the retina of the eyes.
Lord Justice Gage, sitting with Mr Justice Gross and Mr Justice McFarlane, stressed that the appeals had been decided on their individual facts.
The judges ruled that the diagnostic triad of injuries remained valid, but with limitations. The mere presence of the triad did not necessarily indicate NAHI, but the triad had "not been undermined" in the manner suggested by the defence.
Responding to the ruling, the Crown Prosecution Service said: "The judgment sends a clear signal validating the approach used by the CPS in prosecuting shaken baby syndrome cases.
"The CPS will continue to prosecute appropriately in order to protect infants - the most vulnerable victims in our society."
Mr Malone, of solicitors Stephensons, who represented Ms Harris, Rock and Cherry, said: "Mr Cherry is confident that he will be back before the Court of Appeal." He said Ms Harris found it difficult to be happy about the decision to clear her name. Because of her arrest, she was not allowed to go to her son's funeral. "Beyond that, a baby born to her as she started her sentence was placed for adoption."
At least another 89 cases of "shaken baby syndrome" were thought to be awaiting review.
Mother 'devastated' by ruling
Lisa Davis, the mother of baby Heidi, left the court in tears after Raymond Rock's conviction for the murder of the 13-month-old was reduced to manslaughter.
"I am devastated," she said. "What they are basically saying is that you can shake a baby to death and you are not guilty of murder. You only get manslaughter."
Rock, of Great Yarmouth, Norfolk, was serving life for murdering his girlfriend's child in 1998.
He was alleged to have shaken the child violently but he insisted that Heidi had wriggled out of his arms and fell to the floor. Rock was given a new sentence of seven years, and because he has already served six years, his solicitor, Campbell Malone, said he should now be released.
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