Those hopes had been stymied by the fact no body has ever been found, and the controversial end to the trial of three men who were accused of a drugs-world killing of Philip.
Wellington men Danny Condren and Bartley Kelly and former Hawke's Bay man Sonny Crawford were discharged after the judge ruled during their trial in October 2003 that unsound evidence heard by the jury prejudiced the men's right to a fair hearing.
They cannot be charged again, even if the body is found or new evidence emerges.
Mr Cowan later called for the jury system to be replaced by an inquisitorial system and for those who knew what happened to at least reveal where his son's body was. While the family's plight was unusual, families of murder victims and other serious crime generally meet a range of ongoing difficulties they should never have to face.
"People are affected in different ways," he said.
"We don't want anyone to go through what we have been through."
Mr Cowan, an accountant who now volunteers his services to a variety of organisations he hopes can bring change which will lessen the chances of such tragedies occurring, called on society to also search for answers.
Sunday's half-hour remembrance at Memorial Square in Napier was attended by about 60 people, including Kelly Pigott, the mother of Teresa Cormack who was abducted and murdered at the age of 6 in 1987.
Families and friends of other victims and Coleen Davey, who has been involved in organising similar events in Hastings since the early 1990s, also took part.
