Five-month-old Hayley Davidson died at the Royal Hospital for Sick Children in Edinburgh on February 17 2016, three days after she was found at a property in Buckhaven, Fife.
Gordon McKay, 38, admitted killing the infant - his then girlfriend’s daughter - by seizing her body and shaking her repeatedly, inflicting serious head injuries.
McKay, of Buckhaven, was originally charged with murder but pleaded guilty last month to the reduced charge of culpable homicide.
Passing sentence at the High Court in Edinburgh, judge Lord Uist said: “Hayley’s death has caused profound grief to the members of her family.”
Hayley had been left in McKay’s sole care at the time of the assault.
The court has heard that some time after 11am that day, McKay sent the girl’s mother a text, saying “come quick” and she ran along to his house.
She found McKay leaning over her daughter, giving her CPR.
She screamed “what happened?” at him and phoned an ambulance.
When paramedics arrived a short time later, they found the girl’s mother in a distressed state, while the infant was “pale, floppy and unresponsive”.
He told his partner he had given Hayley a shake after finding her unresponsive after she had wriggled down into a beanbag.
The court heard the assault caused the infant to suffer a bleed around her brain consistent with significant head injury caused by shaking.
Lord Uist told McKay the victim was “an innocent, defenceless child”.
He said: “I emphasise that your plea of guilty included an admission of assault by repeated shaking in order to dispel any suggestion that what happened was nothing more than an accident.
“There should be no doubt in the mind of anyone that Hayley’s short life was brought to an end by a criminal act on your part.”
The judge said McKay had also failed to give a true account of what actually happened to the girls’ mother, doctors and the police.
Defence counsel John Scott QC said the “enormity” of what he had done will stay with McKay.
“Mr McKay is very sorry for what happened and still cannot really understand it,” he said.
The court heard that a doctor found the ex-soldier meets all the criteria for a diagnosis of post-traumatic stress disorder (PTSD) following his time in the forces.
“What he has struggled with from the outset is taking in the consequences of what he did, which was not intended and were not foreseen by him,” the QC said.
“What he did was a deliberate act, it was an assault upon this five-month old baby. It was wholly inappropriate.”
Imposing the sentence of seven years and six months, Lord Uist told McKay: “The taking of a baby’s life by an assault involving repeated shaking, even where it does not amount to the crime of murder, is an extremely grave crime which must attract a lengthy sentence of imprisonment.”
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