Eddie Travaglia had finally achieved the happiness he wanted for his disabled sons after a long battle with authorities over their care.
His two sons Leigh, 31, and David, 27, who had cerebral palsy and were profoundly deaf, now had specialised carers who could communicate with them and who took them on outings.
At that time in 2009, those who knew the sons said they were as happy as they had been for a long time.
On August 15 that year, Mr Travaglia picked the pair up from the Mornington Peninsula care facility where they lived and took them to his Rosebud home for the night.
They shared a pizza before Mr Travaglia placed his sons in his Daihatsu station wagon and joined them.
When friends searched for the trio the following day after they had failed to show for a planned meeting, they found the Daihatsu with its engine running and the Travaglias inside - dead from carbon monoxide poisoning.
Delivering a finding on Tuesday into the deaths, Victorian Deputy State Coroner Iain West noted Mr Travaglia had a history of depression, prostate cancer and suicide attempts, but said why he took his sons' lives at that time was a mystery.
"It is puzzling to know why Mr Travaglia decided to take his sons' lives when they were finally enjoying the sort of quality of care he had fought so hard for," Mr West said in his finding.
"In a note dated August 15, 2009, he refers to the boys as a `bargaining tool'. However, there is evidence from those who knew the boys to indicate that it was the happiest they had been for many years.
"Those closest to Mr Travaglia stated that he was a devoted father and hence a possible reason for his actions was that he couldn't accept the prospect of leaving them behind if he wasn't there to protect them."
Mr Travaglia's former wife and the boys' mother, Katrina Blake, who lived in the same street as their father, was in Queensland visiting a sick relative when they died.
In 2003 Department of Human Services housing was found for the Travaglia sons at a facility managed by a private organisation in Mornington.
Initially it went well, but later their parents believed cost-cutting had led to a decrease in staffing and a reduced level of care.
Mr Travaglia felt he had failed, but in February 2009 a new facility was found.
Mr Travaglia wrote in a note in June 2009 that "all is finally good", but added things were not perfect.
In the same note he wrote that he felt his time was up and there was no use being around anymore.
* Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14 or SANE Helpline on 1800 18 SANE (7263).