Convicted of murder and jailed for life in 1997, she was freed 279 days later in a shock ruling when the judge downgraded the verdict to manslaughter.
Twenty-five years on and opinion is still divided about what happened on that fateful day as Louise, then 18, and from Elton, Cheshire, looked after two children at their US home near Boston, Massachusetts.
At her trial, expert prosecution witnesses claimed Matthew’s injuries, including a cracked skull, displayed the “triad” of symptoms consistent with him being violently shaken.
One expert, Dr Patrick Barnes, testified this was the “classic model” of shaken baby syndrome (SBS) and dismissed the defence’s argument that Matthew’s injuries had been sustained at an earlier date.
But in a new Channel 4 documentary, Killer Nanny: Did She Do It?, the medic reveals he has since changed his mind — and says the science behind the diagnosis of SBS is flawed.
In the three-parter, which starts tomorrow, he says: “I was very strong, that it had to be shaken baby syndrome. I can’t (now) give testimony that would convict Louise Woodward beyond a reasonable doubt. I shouldn’t have done that.”