A murdering mum left another child with a fractured skull and ribs - but was never prosecuted at the time, the Post can reveal today.
Baby killer Jennifer Crichton had told professionals about the attack at the time - but a decision was taken that there was not enough evidence to prosecute her.
She was only charged over the historic attacks once a murder probe involving her daughter Amelia began last year.
In addition to finding her guilty of killing her seven month old daughter Amelia yesterday, jurors also found her guilty of committing three counts of Section 18 assault and an offence of child neglect.
The Post has been unable to revel the details until now due to legal reasons.
When baby Amelia was born, several years after the other attack, Crichton, 35, of Slater Lane, Leyland, was permitted to have the care of her, with support from social workers, under a care order by Lancashire County Council.
The authority says it is carrying out a review into its procedures.
Today Detective Inspector Simon Cheyte, of Lancashire Constabulary’s Force Major Investigation Team, said: “Jennifer Crichton has never given a satisfactory account of what happened at the address on that fateful night and we may never know exactly what happened which led to Amelia’s injuries.
"What is clear is that that she suffered catastrophic and deliberate injuries which she could not survive and the only person who could have caused those injuries is Jennifer Crichton.
“The person who should not be forgotten in this is Amelia. She should have been able to look to her mother for the protection and love of a parent. Instead this defenceless child found herself subjected to horrendous abuse and the injuries which led to her death.
“In relation to the conviction for assault on the other child this was subject to a previous police investigation and Jennifer Crichton was arrested but at that time it was decided by the Crown Prosecution Service there was not enough evidence to prosecute her.
"Following the murder of Amelia the earlier assault was reviewed and further evidence, not available to the original investigation team, was discovered. This was considered along with the supporting evidence of Amelia’s sad death and it was decided that charges could be brought and today’s conviction secured.
Yesterday Lancashire County Council released a statement from County Councillor Susie Charles, Cabinet Member for Children, Young People and Schools, which said: "Amelia's death was a horrific tragedy.
"Now that the court case has been concluded, Lancashire Safeguarding Children Board (LSCB) will continue its Serious Case Review (SCR) to find out what the organisations involved can learn.
"We'll provide information about the county council's involvement as part of the SCR and work with LSCB if they identify any areas where we can improve our practices."
Following today's revelations the authority say it will not be commenting further in light of the review. Such reviews are undertaken every case where abuse or neglect is known - or suspected - and a child dies or is seriously harmed and there are concerns about how organisations or professionals worked together to protect the child.
The Post has asked the Crown Prosecution Service to comment.
Crichton will be sentenced on March 11.