A father found to have sexually assaulted his 13-month-old daughter shortly before her sudden death will not face criminal action unless new evidence comes to light.
High Court family judge Mr Justice Peter Jackson has ruled that 48-year-old Paul Worthington - on the balance of probabilities - "perpetrated a penetrative ... assault" on daughter Poppi.
Poppi collapsed with serious injuries at her home in Barrow-in-Furness, Cumbria, in December 2012 and was rushed to hospital where she was pronounced dead.
But Cumbria Police conducted no "real" investigation for nine months, the judge found, as senior detectives thought a pathologist "may have jumped to conclusions" in her belief the child had been a victim of abuse.
The toddler was buried in February 2013, precluding a further post-mortem examination, after her body was released by the local coroner.
There is now said to be an "absence of evidence'' to find out how Poppi died, or definitively prove if or how she was injured.
Mr Worthington was arrested in August 2013 and questioned on suspicion of sexual assault but was not charged with any offence. He strenuously denies any wrongdoing.
The Crown Prosecution Service (CPS) has previously said it conducted "a thorough review of the evidence" but decided it was insufficient to provide a realistic prospect of conviction.
Poppi's death had been shrouded in secrecy, with a 2014 fact-finding civil court judgment being kept private so as not to prejudice any criminal proceedings, while an inquest controversially took only seven minutes to declare her death as "unexplained".
During the civil proceedings it emerged that Mr Worthington watched pornography on his laptop in bed in the hours before his daughter's death, which he described as "involving adults".
It was also revealed that he was informally interviewed by police in 1995 over his association with someone who may have committed offences against children, while in 2003 he was the subject of an unrelated allegation which was later retracted.
Sitting at Liverpool Crown Court, Mr Justice Jackson handed down a second fact-finding judgment as part of care proceedings in relation to other children in the family - after Mr Worthington successfully appealed for a review of the 2014 medical evidence.
He arrived at the same conclusion as in 2014 as he said Poppi's "significant bleeding" within 15 minutes of the 999 call could only be sensibly explained as the result of penetrative trauma, and that Mr Worthington was responsible for that.
Cumbria Police reiterated that "lessons had been learned" from the case.
Three officers were investigated by the Independent Police Complaints Commission (IPCC) after a self-referral from the force, it added.
One officer - believed to be former Detective Superintendent Mike Forrester - was suspended and has since retired, the second was dealt with by management action and the third is undergoing "performance proceedings".
Last July, High Court judges ruled that a second inquest into Poppi's death should take place after the original hearing in October 2014 called no evidence, as then coroner Ian Smith indicated he had taken account of and adopted the 2014 findings.
The CPS has said that if any new evidence arose at the second inquest it would "consider this carefully with the police".
Mr Justice Jackson noted in the judgment that the part of the inquest record headed "How, when and where the deceased came by his or her death" was left blank.
A spokesman for the NPSCC said it was "deeply worried and angered by this shocking case" and that "no child must ever be failed again in this way."
He added: "A vulnerable baby died after suffering appalling injuries, and there were clearly serious and inexplicable failings in the investigation into her death.
"It's vital we get a full understanding of the circumstances that led to officers not following basic procedures, not securing forensic evidence and delaying their inquiries.
"There were also huge problems in the way this case was been handled by other agencies, which could have left other children at risk of serious harm."