Ronald McManus, also known as Ronnie Dunbar, of Rathbraughan Park in Sligo, was found not guilty of murder but guilty of the manslaughter of the 14-year-old schoolgirl in September 2006.
At his sentencing hearing today, Mr Justice Barry White asked lawyers for the prosecution to remind the court of the attitude of the Mahon family when Melissa went missing in 2006.
The court heard that they were uncooperative with gardaí and initially declined to make a statement that she was missing because her mother said she was in the care of the HSE at the time.
Mr Justice Barry White said the victim impact statement was therefore 'disingenuous in the extreme' in his view.
In the brief victim impact statement, which was read by counsel for the prosecution Isobel Kennedy, the victim's mother Mary Mahon said she and her daughter Leanna, who was closest to Melissa, had attempted suicide. She said 'Melissa was her baby and her whole life had been torn apart by her death'. She said it had had an emotional effect on all the family.
Counsel for Ronald McManus told the court that the nearest parallel for sentencing was the case of Wayne O'Donoghue.
He told the court it was clearly a case of involuntary manslaughter.
Brendan Grehan said it was all very well for the DPP to say it was at the higher end of the scale for this type of offence but he said he had to ask: what exactly was this type of offence?
He said in returning a verdict of manslaughter the jury was satisfied that Ronald McManus did not intend to kill or cause serious injury.
However Isobel Kennedy for the prosecution said the difference between this case and the Wayne O'Donoghue one was that there was a high level of remorse shown in the O'Donoghue case and an assertion that it was an accident.
Previous convictions
The court heard that Ronald McManus had a number of previous convictions in Ireland and the UK for burglary, assault and theft.
The trial heard he strangled the schoolgirl and dumped her body in the River Bonnet in Sligo.
Melissa Mahon had been in the care of the State, living voluntarily in a care home in Sligo. She had run away from care a number of times and had begun a relationship with Ronald McManus who allowed her to hide from gardai and social workers in a vacant house next to his.
Her friends said that before she went missing she was pregnant.
A year and a half after her disappearance Ronald McManus's teenage daughters told gardai that their father had killed Melissa. Her remains were found on the shores of Lough Gill in February 2008.
Both daughters gave video link evidence at the trial and said their father had strangled Melissa in his bedroom and forced them to help him dump her body.
The trial lasted five weeks during which McManus denied the charges. The jury reached a unanimous verdict of not guilty of murder but guilty of manslaughter.
The sentence hearing at the Central Criminal Court has been adjourned until Friday.
