Mystery still surrounds the exact circumstances of how a four-month-old baby died, a coroner has said.

Kayleigh-Mai Sheard was pronounced dead by paramedics who had been called to her parents’ home in Foldings Avenue, Scholes, Cleckheaton , in the early hours of September 30, 2013.

They found her seated in a bouncy chair close to a gas fire that had been turned to its highest setting. Kayleigh-Mai, who was covered in Sudacrem, was cold, not breathing and unresponsive. In addition she had suffered extensive burns to her face that had caused charring and skin loss.

In interviews with police neither Kayleigh-Mai’s mother, Lucy Damen, 22, nor her father Daniel Sheard, 24, could account for their daughter’s injuries, with Sheard blaming the burns on sunburn caused by recent hot weather. He said other injuries had not been caused by either him or Damen. However the police found no evidence of third party involvement.

Daniel Sheard (left) and Lucy Damon (right) who were convicted of cruelty by neglect in connection with the death of their daughter Kayleigh-Mai

Both parents were jailed at Leeds Crown Court for their “wilful neglect” of their daughter.

Sheard was found guilty of cruelty to a person under 16 and was sentenced to six years in prison. Damen received four-and-a-half years. She admitted the offence.

Kayleigh-Mai’s parents remain in prison. No other family members attended the inquest.

A joint paediatric and forensic post mortem on Kayleigh-Mai’s body revealed she had suffered extensive injuries including bruises, abrasions, scars and fractures to her upper right arm, collarbone and a rib. Reports by a team of medical professionals, including paediatric consultants, a consultant radiologist, a consultant neuropathologist and a consultant paediatrician, found no evidence of significant viral infection, natural disease, meningitis or encephalitis or evidence of a skull fracture or a predisposing bone disorder.

No evidence was found to suggest that Kayleigh-Mai had been shaken or had died as a result of being shaken.

Burns specialist Dr Simon Myers said the injuries to Kayleigh-Mai’s face were consistent not with sunburn but with burning from close proximity to a gas fire. He added that burning was unlikely to have been the primary cause of her death but may have contributed to it.

Dr Kathryn Ward, a consultant paediatrician, found no evidence of outlying medical conditions that could have contributed to Kayleigh-Mai’s death and that her bone fractures “were consistent with non-accidental injury.”

Foldings Avenue in Scholes, Cleckheaton where Damen Sheard and Lucy Damon lived and where Kayleigh-Mai's body was found.

The inquiry into Kayleigh-Mai’s death was led by Det Supt Simon Atkinson, of West Yorkshire Police, who said the injuries she had suffered were non-accidental and “incompatible” with her parents’ account.

“We could not see anybody else that could have been responsible for those injuries,” he said, adding that the investigation team was “satisfied they occurred in the family home.”

He said there had been no “red flags” in Kayleigh-Mai’s background to raise concerns although neighbours had reported hearing raised voices from the parents and the loud crying of a child.

“It is a matter of great regret from those neighbours that they did not call the police,” he added.

West Yorkshire Assistant Coroner Kirsty J. Gomersall described the case as “a tragedy of immense proportions.”

She said it was the view of medical experts that the diagnosis of Sudden Infant Death Syndrome could not be applied and that no cause of death could be established.

She added: “While it is clear that Kayleigh-Mai had incurred extensive injuries prior to death, my role as the coroner is to ascertain the cause of her death, which I find to be unascertained. I return an open conclusion.”