The hearing had brought closure in the sense that the formalities were over at last.
"But finding his body is ongoing. The whole process has just been traumatic for our family."
Mr Cowan, an accountant who volunteers his services to a number of organisations, accepts his son is dead and has his own theories of what happened.
He said he would fight for a review of the criminal justice system but was not ready to talk about those plans.
"It's early days."
Mr Cowan has also asked Coroner Garry Evans to consider making recommendations to help parents prevent other drug-related deaths. Suggestions he made were "more contact with your kids," drug education, counselling and legalising cannabis - "although I don't personally favour that one".
The Cowans' grief was obvious at the inquest, where Simon Cowan talked fondly of Philip as a child growing into a young man and his wife walked around, weeping silently, showing a photograph of him to those present "so you can see what he looked like".
During the hearing, Mr Cowan was rankled by a lack of information, including in relation to a 2003 jury trial of three men charged with Philip's murder.
The prosecution called 124 witnesses during the 10-week trial but the jury did not get to decide guilt or innocence. The presiding judge discharged the accused, ruling that unsound evidence was "contaminated and unsafe", prejudicing the trio's rights to a fair hearing. The discharge served as an acquittal and they cannot be charged again.
Coroner Evans said he was constrained by the law and could only make his findings on what was before him. The High Court was "the superior court".
Giving evidence, Detective Senior Sergeant David Thornton said Philip Cowan, who lived in Hastings, had travelled to Wellington on March 19 or 20, 2001, where he had cannabis stored.
On March 31 his car was found abandoned in Bulls. A police investigation continued for more than two years.
There was no new evidence, but police did not believe Philip Cowan would have planned his disappearance and were convinced he was dead. He had a new relationship, a goal of being a millionaire by aged 30, and cannabis plantations ready for harvesting.
His body may have been buried in the Tangimoana Forest near Bulls but without a specific location, it was too large an area to search, Mr Thornton said.
The coroner indicated his finding would be that Mr Cowan died on or about March 5, 2001, at the hands of a person or persons unknown, his body destroyed, irrecoverable or lost, and that the place and cause of his death were undetermined.
The written findings would be released in the next two weeks.
To the coroner, Simon Cowan said he felt like a failure.
"Seeing your son die you don't feel like a good father. How do you prevent deaths like this?"
And he says remembering his son is hard.
"I lie in bed at night and think about Philip. Tears run and I try not to wipe them away, to be staunch."
