Police who wrongly accused a grieving mother of murdering her own son and dumping his body in woodland had become "fixated" on her being responsible, a senior investigator has said.
Ruth Neave was charged with the murder of her six-year-old son Rikki Neave after his disappearance on 28 November 1994, and went on trial two years later.
She was acquitted by a jury but has spoken of how the cloud of suspicion cast by the charge followed her for decades - until James Watson was on Thursday convicted of Rikki's murder, having evaded justice for more than 27 years.
Watson, who was 13 at the time he killed Rikki, was convicted by majority verdict by a jury at the Old Bailey, who spent more than 36 hours deliberating over a period of two weeks.
The officer who led the successful investigation said Cambridgeshire Police detectives in the original murder probe had focused on Ms Neave, who was later jailed after admitting child cruelty charges, and that modern techniques had eventually led his team to the real killer.
Former assistant chief constable Paul Fullwood also revealed the force had apologised to Ms Neave and Rikki's family for how long it had taken to get the case to court.
"They were very much fixated and focused on Ruth Neave," he told ITV News Anglia, reflecting on the original investigation.
"You can understand why she came on their radar. But by today's standards, that just wouldn't have happened in 2015 [when the new investigation was launched].
"We have had to be far more open-minded."
The cold case team looked at the evidence with “fresh eyes” and found lines of inquiry that had not been followed up and expert witnesses never used.
They including a soil expert who examined Rikki’s muddy shoes and concluded he had walked into the woods where he was found dead but not walked out, contrary to the “fanciful” theory that his mother wheeled him in a buggy.
Mr Fullwood said finding Rikki's killer had been one of the biggest challenges in the history of the force, surpassed only by the investigation into the Soham murders of Holly Wells and Jessica Chapman.
The new investigation involved taking 1,500 witness statements and analysing around 15,000 documents - around three times more than would be expected on a case of the scale, said Mr Fullwood.
Mr Fullwood continued: “And then once we started our reinvestigation, we were faced with the challenges that all the original exhibits have been either destroyed or been given back to the family.
“Thankfully, we were able to recover tapings from Rikki Neave’s clothing.
“We were able to take a forensic analysis and that’s where we found DNA, one billion to one, which pointed us towards James Watson. But that in itself is not enough.
“We then started looking at James Watson in far, far more detail and realised that there was more to this individual than meets the eye.”
Having been discounted quite early in the original investigation, the fresh probe uncovered a “pattern of lies” about his movements on the day Rikki disappeared.
Witnesses came forward with disturbing details about his fascination with dead animals and sexual interest in young children while an ex-girlfriend, whom he met after the murder, said he had strangled her during sex.
Mr Fullwood said: “The more we looked at James Watson, the more convinced we were that he was the person responsible for the dreadful murder of Rikki.”
Despite the damning DNA evidence, the Crown Prosecution Service initially decided there was “insufficient evidence” to go to trial but reversed the decision after the family challenged through the victim’s Right to Review Scheme.
There were further delays after Watson was extradited from Portugal, meaning his trial could not start until 2022.
Mr Fullwood said: “All the way through this it’s been a monumental series of challenges but, as far as we’re concerned, we’ve got the right person responsible for the dreadful, dreadful murder of that little boy Rikki Neave.
“Rikki Neave was brutally murdered, strangled, stripped of his clothes, left in the wooded area.
“Hopefully, we can bring some justice for his family… and also make sure that we put a dangerous individual in prison.”