A couple said to have swapped the identity of their dead baby daughter to her twin sister in a bid to conceal a catalogue of injuries they caused have been found guilty of child cruelty.
The seven-month-old was rushed to hospital after her parents reported she had breathing difficulties and was pronounced dead shortly after.
The Crown said Mohammed Karolia, 29, and his wife Nafisa, 22, told medics at Royal Blackburn Hospital that she was the healthier and smaller of their identical twins before they allegedly later switched to naming her sibling on the death certificate.
Preston Crown Court heard the defendants made a deliberate attempt to hide the ailing twin from the outside world in the weeks leading up to her death in June 2009.
The couple denied any baby swap, which was described as "fanciful" and "far-fetched" but the jury today convicted them of the offences.
The jury reached its decision after less than six hours of deliberation following a five-week trial.
Remanding the couple in custody, Mr Justice Irwin told them: "You will both inevitably face considerable prison sentences.
"As you know, this was a bad case of child cruelty. However, I want to know as much as possible about it before deciding the length of sentence."
He adjourned the case for pre-sentence and psychiatric reports.
The hearing will take place on a date to be fixed in October.
Joe Boyd, prosecuting, said the identity swap was uncovered by discrepancies in the head, weight and height measurements previously taken from the twins - known as Twin M and Twin A for legal reasons.
Members of the jury were told they did not necessarily have to believe the twin swap theory to return guilty verdicts.
Twin M had suffered numerous injuries including fractures to the ribs, legs and arms, and skull damage affecting the brain and central nervous system, the prosecution said.
She also had a mouth ulcer, unexplained scratching to the ears, bleeding in the eyes and injuries to the nose. The victim's nasal injuries were particularly "unusual" with damaged tissue suggesting her nose had been pinched with equal force on both sides by a clasp or clip.
The broken bones were said to have taken place between 24 hours and six weeks before death, while a post-mortem examination found she died of bronchopneumonia.
In opening the case, the prosecutor said the Crown did not seek to prove any maltreatment by the parents caused the baby's death but said they had never provided a plausible explanation for the injuries.
The victim had only ever been out of their care for a matter of a few hours in her short life.
He said theoretically the injuries sustained could have been accidental but the number, the timescale and the lack of explanation for them "leads inexplicably to the conclusion they were inflicted deliberately by one or both of the parents".
Explaining the alleged twin swap, Mr Boyd said: "The living twin's progress is consistent with that of Girl A, while the dead twin's progress corresponds to Girl M.
"Growth charts for both twins make it clear that the parents have at some stage swapped the babies. They have very probably done so to seek to conceal the mounting injuries being suffered by the child who died - always the bigger twin but, for some reason, rejected and abused by them."
Mr Boyd said the couple had tricked a number of visiting health professionals into thinking they were seeing Twin M. He added that neighbours had only ever seen the Karolias with one baby and there was nothing to indicate they had twins.
When interviewed by police Mrs Karolia said she noticed nothing unusual about her daughter apart from a runny nose. She also told detectives she was doing a course on childhood studies as she wanted "to do something with kids at a later stage".
Her taxi driver husband told officers his wife was the principal carer of the twins and he too identified no problems aside from a runny nose, the court heard.
The defendants, of Meadow Close, Blackburn, had each denied the offences which took place between November 26 2008 and June 16 2009.
Outside court, Detective Inspector Pete Broome described the investigation as "one of the most extreme cases I have come across".
He said: "I can only describe this as a bestial crime - that is what they are, beastly.
"The only two people who know if these babies were swapped over are the parents. Therein lies some of the worst aspects of this case because the surviving twin may never know who she really was at birth.
"That must be the most corrosive aspect to come out of this case.
"The prospect of not doing anything to an injury like that to a child's nose is abhorrent and I cannot understand anybody worthy of the name parents could leave a child suffering in that manner."
Neither of the twins were known to social services.
Linda Clegg, Blackburn with Darwen Council's director of children's safeguarding and protection, said: "This is an extremely sad and tragic case, it has been distressing for all concerned.
"All the usual procedures that the council has to carry out in relation to the child's death have been fulfilled by the local authority and its partners and we are continuing to support the welfare of Child M's sibling."