Baby P died from abuse despite 60 visits from authorities
Police mistakes meant a chance to charge Baby P's mother with assaulting him was missed several weeks before his death, an unpublished report says.
Delays securing an independent medical opinion meant the six-month legal deadline passed within which to charge the mother with common assault.
The report into what happened to Baby P before his death in August 2007 found several police errors.
The Metropolitan Police said it could not comment for legal reasons.
Lynne Featherstone, Liberal Democrat MP for Hornsey and Wood Green, said there had been a "monumental failing" by the police.
The toddler was first taken to Whittington Hospital with extensive bruising in December 2006.
Doctors thought the injuries were suspicious and the child was put on Haringey Council's child protection register.
The review, by the Haringey Safeguarding Children Board, found police did not photograph his bruises for a week and failed to photograph his home, a potential crime scene.
Furthermore, the review found that officers did not visit the home with the social worker and kept no detailed notes of conversations with the mother.
There is no accounting for poor, sloppy police investigation
Valerie Brasse, Metropolitan Police Authority
The Crown Prosecution Service asked police to get an independent medical review of the toddler's injuries. A specialist was identified to carry it out.
But in March 2007 the detective in charge transferred to a different part of the Metropolitan Police without formally handing the case over to another officer in breach of standard operating procedures.
With no officer allocated to the case for two months, the investigation "drifted".
The review said: "This might have made it more likely that all the subsequent incidents were reported to the police and that arguably the child might have been more effectively safeguarded."
Valerie Brasse, a member of the Metropolitan Police Authority and an adviser to the Victoria Climbie Inquiry, said the findings were "appalling" and "not acceptable".
"There is no accounting for poor, sloppy police investigation and if that is what is emerging then that is a poor investigation.
"The issue remains though that if an investigation is poor and of that quality, what then the role of the supervisor and why wasn't that picked up?"
The report shows a number of mistakes by police
An opportunity to revive the police investigation was missed when, in April, Baby P was taken to hospital again with more bruising.
Social workers did not inform the police, believing the doctor did not suspect abuse. But the Serious Case Review said they should have alerted officers.
In June 2007, when Baby P was taken to hospital yet again with extensive bruises and scratches, his social worker did contact police.
Baby P's mother was arrested but again it was a week before photos were taken of the boy's injuries and police did not talk to his older siblings.
And the review questions why the mother was not asked - at interview - who else was living in the family home.
This might have shed light on the presence of her boyfriend, the man now convicted with her of having caused or allowed the death of Baby P.
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