A catalogue of police failures over the death of a 13-month-old girl has been laid bare by the Independent Police Complaints Commission (IPCC).
Poppi Worthington died in 2012 with a family court judge finding she had been sexually assaulted by her father Paul, who denies any wrongdoing.
Cumbria Police allowed evidence to be thrown away, failed to properly investigate abuse claims and sent incorrect information to the coroner.
The force said it had "let Poppi down".
The 92-page IPCC report is particularly critical of the two lead officers in the case, both of whom have since retired.
The IPCC said Det Insp Amanda Sadler, who initially led the investigation, and Det Supt Mike Forrester who took over, had cases to answer for gross misconduct.
Det Supt Forrester retired before any action could be taken. Det Insp Sadler was demoted and then left the force.
They are criticised for their failure to preserve evidence and failing to properly ascertain Poppi's cause of death from two pathologists who gave conflicting reports.
The IPCC said the reason the case remained unresolved was because they had an "unstructured and disorganised approach" and "did not conduct a criminal investigation despite there being significant suspicious circumstances from the outset".
What did Cumbria Police get wrong?
- Officers allowed a relative to throw Poppi's nappy away; a "crucial piece of evidence" according to the IPCC
- They failed to get a clear idea of the cause of death
- The first pathologist's eventual report saying Poppi's death was an "unlawful act" took six months to come through
- Det Supt Forrester said his job was to investigate how Poppi died, not if she had been sexually abused
- Junior officers felt frustrated and "kept out of the loop" during the investigation
- The IPCC criticised police for being reluctant to arrest Poppi's parents at such a sensitive time despite having suspicions the girl had been assaulted
- Samples were taken from Mr Worthington but there was a delay in sending them for analysis
- Detectives failed to use proper police logging systems throughout the investigation and instead relied on email
- A form sent to the coroner contained incorrect information, copied from a previous form, claiming Poppi had not suffered any injuries
- Police failed to notify the watchdog of critical failings highlighted by the family court
- Det Insp Sadler blamed delays in the initial investigation on the fact the death happened near the weekend
- She also said she was inexperienced, but the IPCC said she had been in the police for more than 20 years so "it was not clear what was new to her"
- Various other procedures were not followed throughout the investigation
One pathologist said Poppi's injuries provided evidence she had been abused.
But police disregarded her report saying she may have "jumped to conclusions" because Det Insp Sadler had told her abuse might be an issue before the post-mortem examination took place.
A second pathologist said Poppi's injuries had natural causes. The IPCC criticised Det Insp Sadler for failing to clarify the cause of the death.
Mr Worthington, who had been the last person looking after Poppi, was arrested eight months after her death but no charges were brought.
Irwin Mitchell solicitors, speaking on behalf of Poppi's mother who cannot be named for legal reasons, said the child's mother was "understandably deeply concerned by the findings of the IPCC".
"She has anxiously awaited answers as to what happened to Poppi on that fateful day," the company said.
"To learn that the actions of senior investigators within Cumbria Constabulary may have contributed to the agonising delays she has endured has left her deeply and profoundly disappointed and distressed."
Cumbria Police's chief constable Jerry Graham said he "unreservedly" accepts the criticisms and is "absolutely clear the investigation fell well short of the expected standard".
He said: "I profoundly regret that we let Poppi and her family down and I offer a heartfelt apology for this."
A second inquest into Poppi's death is due to resume before the end of June.
Her first inquest ended after seven minutes with the cause of death being "unascertained".