The child was two years old at the time of his death
Look at Kyle Fisher's right eye. Behind his drooping eye was a damaged brain.
Look at his head. It was abnormally big.
Babysitter Suzanne Holdsworth - free today after a retrial - spent three years in prison after she was convicted in 2005 of murdering Kyle because of this simple logic: Kyle was essentially healthy, then he was killed.
The simple logic was wrong - Kyle's brain had five separate disorders - and that mistake led to a terrible miscarriage of justice.
That miscarriage only became clear when Newsnight reported on it a year ago when Ms Holdsworth was still in prison, and was only righted when a jury at Teesside Crown Court found her not guilty.
After Ms Holdsworth, 38, was convicted in 2005, Cleveland Police boasted of "a relentless investigation" led by Det Supt Tony Hutchinson, the now retired "super cop" who nailed "canoe man" John Darwin.
Far from being relentless, too many things that should have been investigated properly were not investigated.
Ms Holdsworth was alleged to have smashed Kyle's head against the banister at her home.
But there was no visible blood, no hair, no skin on the banister, and no DNA test was carried out.
The accused's partner, Lee Spencer, who has stuck by her throughout, told me: "They didn't do a DNA test on the alleged murder weapon.
"I'm no Sherlock Holmes, I drive a cement mixer, but what kind of investigation was that?"
The babysitter said in her frantic 999 call that Kyle was suffering from a fit - and never changed her story.
Home Office pathologist James Sunter, now dead, reported after the toddler's death in July 2004 that Kyle's brain was essentially normal - one of eight findings he got wrong.
New defence experts like neuro-pathologist Dr Waney Squier and Professor Bill Dobyns from Chicago University say that Kyle suffered five separate brain disorders.
They were: scarring caused by the brain pressing down through the hole in his eye socket onto his eye; an abnormally big brain; brain matter in the wrong place; bleeding on the brain; water on the brain.
Suzanne Holdsworth always denied killing Kyle
Any one of the five can cause a fit or epileptic seizure and, as Dr Squier told Newsnight a year ago, "seizures can kill".
The eye injury that caused Kyle's brain to scar has never been properly investigated by Cleveland Police.
It happened in March 2003, when Kyle allegedly fell from his pram on to a fire prong, which punctured his eye socket and stabbed his brain.
It happened while he was in the care, not of Ms Holdsworth, but of his mother, Claire Fisher.
The retrial heard evidence that four nights before he died Ms Fisher left Kyle home alone, locked in a bedroom by tying a belt to a broom handle to block the door.
Ms Fisher admitted that she had been a negligent mother.
The court heard evidence that Ms Holdsworth was, in contrast, a caring mother to her two daughters, Leslie and Jamie-Leigh, who have never questioned her innocence.
Both women deny causing bruising to Kyle's head on the night in question - but it could have been caused while Kyle suffered an unseen fit.
Early on, Cleveland Police decided that the eye and brain injury was irrelevant to the murder inquiry though the police say they relied on the opinion of the Home Office pathologist.
Kyle's medical notes showed that two surgeons had planned to operate on Kyle's injury.
Newsnight understands that in mid-August 2004, Det Con Paul Hook logged a phone call with James Cook University Hospital brain surgeon Sid Marks.
The two men were said to have discussed the brain injury and at the end of the call Cleveland Police continued to believe the eye injury was irrelevant.
But Mr Marks has no recollection of the call and said that he would never discuss the death of a patient with a stranger over the phone.
Cleveland Police say that the detective was only given the task of logging and reviewing the medical records so these could be assessed by the pathologist.
What is clear is that Cleveland Police did not take statements from the two surgeons in the context of a murder inquiry - a gross lapse in normal police procedure.
Chief Supt Mark Braithwaite told Newsnight: "I am satisfied that Cleveland Police carried out a thorough, diligent and professional investigation and that the prosecution of Suzanne Holdsworth was properly brought on the basis of the available evidence."
Suzanne Holdsworth is now free to spend her first Christmas at her home, with her family, after three Christmases inside for a crime she did not commit.
John Sweeney, who reported this story for BBC2's Newsnight, has helped free or clear the name of eight people falsely accused of murder or manslaughter. His latest report will be on Newsnight tonight at 22:30 GMT on BBC2.
Update September 2011: The Independent Police Complaints Commission published a summary of their inquiry in June 2011, finding that Cleveland Police had investigated the case properly. A story on those findings
can be found here.