"You never get over it."
The one small positive, Arlene says, is they were spared the ordeal of a homicide trial and, in a few years, parole hearings for John Mowatt.
Coroner Katharine Greig's report leaves no room to doubt Mowatt was the killer.
"Had he lived he would have faced serious criminal charges, murder charges, on two counts," Arlene said today.
"He chose to end his life himself and didn't have the guts to face up to what he'd done and many people think, and I do in these terms, that that was cowardice."
But there's one thing about that. If he were to face charges and go to jail then my children and my grandchildren have to go through parole hearings when it came time to come out. They have been relieved of that.
"Arlene said she felt for families who had to endure such hearings.
"That must bring back terrible memories every time. That's one bit of relief [for us].
"Today should have been one of new beginnings for Arlene, as it's her last day as a teacher before retirement.Instead, it's the day a coroner's report into her son's death is made public.
Until Trevor's death, she and husband Graeme never thought something like this would happen to their family.
One of three siblings, Trevor was an active man with three children and a lot of living to do.He's remembered as gentle, kind and diligent.
He was a wonderful child who grew up to make his parents proud.
"He had another good 30 years of life in him," his mother said.
"He wanted to see his children grow to adulthood. He was keen on his rally driving and wanted to do more of that and he wanted to do more exploring of the world.
"He's now missing all of that. He's missed this whole big patch of his life through this man's selfish act. It's shattered and changed our family forever."
A trip to Nepal was on the cards. He was still a fit man too, turning out in social cricket and football matches.
Trevor was a long-time employee at Vero. An accountant, he had also worked at the Manukau City Council and Dominion Breweries after gaining a Bachelor of Commerce.
He began that aged 29 on his homecoming from a London OE.
Arlene said her son had grit and determination, and it had rubbed off on his children.
But Mowatt's actions are a millstone around the whole family's necks.
"I and our family have a lot of anger at Mr Mowatt because this appears to be a very deliberate act," Arlene said.
"He will never ever be forgiven by us."
Coroner Greig didn't make any recommendations in her report, but Arlene would like to see something done to make it harder for New Zealanders to build up a cache of weapons, as Mowatt did.
Why, she wonders, do most people need these high-powered military-style guns? And why is it so easy to get them when all that's needed is a gun license?
"It's just too easy. You can have a whole arsenal at home."