The day after his death, in April 2001, he was to face an operation to overcome a chronic ear infection that would leave him deaf for three months and take away his only link to the outside world. It would permanently reduce his hearing to 10 per cent, at best. According to a police statement, the couple said "they decided that they could not subject [him] to any further pain, and knew in their own minds that the operation [he] was to undergo would take away his quality of life".

Yesterday the couple's lawyer, Tony Bellanto, QC, told the court they should not be jailed for the act "born out of love", but should be treated with compassion and mercy. From the age of five Matthew Sutton lived in institutions but regularly went home on weekends. The court was told that at 18 he moved to a group home in Katoomba, run by the Department of Community Services, where he was frequently physically and verbally abused by staff and other residents. His behaviour changed and Matthew became violent and hard to manage. Furniture and fittings had to be screwed down to prevent him throwing them. The Suttons' family and friends no longer visited when he was at the couple's Leonay home.

Margaret Sutton, 60, who battled to improve conditions in the group home, had two nervous breakdowns and was diagnosed with post-traumatic stress disorder. Her 63-year-old husband turned to alcohol. The couple filled their son's "last weeks of hearing" before the impending operation with everything he enjoyed: a visit to the beach, a trip on a Harley-Davidson and rides on the escalator at a shopping centre.

The day before the operation the couple discussed their son's prospects and made their plan. Margaret Sutton told police afterwards she gave her son some tablets to sedate him, so that "a further act could take place to end his life". She said she did not know what it was, and was not with him when he died. Raymond Sutton told police he later went to his son's bedroom and "released" him from this world. He did not want to tell police what he did but agreed the act he performed caused his son's death. An inquest heard Matthew's body contained traces of tranquillisers, and suffocation could not be ruled out, but no cause of death could be determined.

Margaret Sutton yesterday told the Supreme Court the couple had their bags packed and their coats ready, expecting police to arrest them immediately. But police did not have proof until the couple confessed in July 2005. They were initially charged with murder, but pleaded guilty to manslaughter.

Crown prosecutor Patrick Barrett yesterday called for the couple to be jailed, "however short", because their joint act was planned and deliberate. "As significant as reasons were in this case for the taking of Matthew's life, the criminal justice system must denounce that conduct in a significant way," he said. The couple will be sentenced later.