It seems an odd approach, given that McKay and his former common-law wife, Samantha Kematch, had already been charged with first-degree murder in the death of Phoenix Sinclair, Kematch's daughter.
The jury in their trial has already heard that the child's life was a misery of beatings, starvation and isolation. They've heard she died alone in the family's basement, was wrapped in a sheet of vinyl, taped tightly in, and then covered in, a yellow raincoat by her mother and stepfather.
They've heard that McKay carried the child's body to his car, placed the corpse in the trunk and drove, along with Kematch, to bury Phoenix in a shallow grave at the Fisher River Reserve dump.
Some of the most damning testimony to date has come from McKay's two sons.
Monday, the jury listened to a three-year-old RCMP audiotape as investigators tried to convince McKay to lead them to the child's remains.
They didn't appeal to him as the stepfather of Phoenix. They appealed to him as the father of the two boys, both of whom were suffering emotionally because their father refused to say where the child's body was hidden.
It had all the markings of a Greek tragedy: Reveal where you buried the dead stepdaughter in order that your children can be set free from their own demons.
The queer thing is, it worked.
McKay had already drawn a rough map of the approximate area where the body was buried. But the RCMP wanted an X to mark the precise spot. Without McKay's help, they'd be digging for weeks or months before they found Phoenix's remains.
They assured McKay they didn't think he was "a monster guy" and said all they wanted was to make sure Phoenix had a proper burial.
Then they found the right nerve to pick.
"There's no closure for the boys," said one investigator, telling McKay his sons would be in agony while the search for Phoenix dragged on.
On the tape, McKay said he wants to talk to Kematch. He began to weep. He was afraid he'll never see his sons again. He doesn't mention not seeing Phoenix again.
The investigator was sympathetic but firm.
"Your boys are going to be OK as long as you love them," he soothed. McKay has control over the future of his boys' mental health, he said.
"You have a chance to do something good for your kids," he said. "It's not what you did. It's what you did after."
In fact, it's what McKay and Kematch are accused of doing that matters.
It's the abuse and slaying of a little girl. But that doesn't come up on the audiotape.
The investigator told McKay he thought the boys were heroes for disclosing the killing of Phoenix to their mother and to authorities.
He tossed McKay a bone.
If he tells authorities where Phoenix is buried, "maybe they can see you as one."
This is a story sorely lacking a hero. You've got a child with a lifelong CFS history, one marked by a file opened and closed several times. The denouement came when a CFS worker, acting on a tip, went to see Kematch but left without seeing Phoenix.
You've got two adults who, according to the testimony of the McKay boys, abused Phoenix with relentless vigour. Although McKay says on the videotape that he still loves Kematch and believes she loves him, that worm has turned too.
The former couple, who share the prisoners' box, are pointing the finger of blame at each other now. Kematch sat Monday with her back deliberately turned to her former lover.
Hero? It's tough to know what McKay's sons think of him now or what they'll think of him in the future.
If the word is going to be used, though, let's apply it to the two boys with the courage to tell the truth about a little girl's fate.