John Salmon doesn't like to talk about the night more than 40 years ago that led to his incarceration for the death of the woman he loved.

The 75-year-old retiree will gladly discuss his cats (five in all), his views on healthy living (eat fish once a day, take karate classes) and various Casino Rama shows he's attended (Kellie Pickler, Jeff Foxworthy, many others). But start prying into the tragedy that landed him with a manslaughter conviction in 1971 and Mr. Salmon' s memories are gone.

On Monday, in a triumph of Mr. Salmon's quiet determination to clear his name through the Association In Defence of the Wrongfully Convicted (AIDWYC), the courts are expected to expunge the events as well.

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"For our children and grandchildren to know, once and for all, that John is the man he is, not the man some people think he is, that's amazing," says his wife, Margaret Salmon, who does much of the talking for him.

The Crown is recommending acquittal almost 45 years after pursuing his conviction based on flawed forensic evidence stating Mr. Salmon had delivered a "terrific" and fatal blow to Maxine Ditchfield's head.

In 1971, Mr. Salmon was a piecemeal welder who lived with Ms. Ditchfield and her three kids in a small Woodstock, Ont., home. On Sept. 19, a Saturday night, the family visited some friends.

It was a raucous, booze-sodden night of dancing and quarrelling. When Ms. Ditchfield fell off her stool after 3 a.m., the couple decided it was time to pack up the sleeping children and drive home, according to documents filed in court.

The next morning marked the beginning of a precipitous and mysterious decline in Ms. Ditchfield's health. She was clumsy, falling in the bathroom. Her body was covered with bruises, the previous night's alcohol consumption clouding any memory of how they got there.

Mr. Salmon spent the next two days trying to nurse her back to health, but after a series of falls, her condition deteriorated. He called a doctor, who visited the house and determined that Ms. Ditchfield's bruises, fixed pupils and laboured breathing suggested brain damage from a wicked beating.

The doctor phoned an ambulance and the police. The former took Ms. Ditchfield to the hospital, where she died the next morning; the latter took Mr. Salmon to jail.

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There were witnesses, but they were either too inebriated at the time or too young – as in the case of Ms. Ditchfield's children – for their testimony to be entirely credible. In that reliability vacuum, an autopsy would be relied upon to determine the central question of whether her puzzling demise was the result of an assault or natural causes.

The autopsy noted "bruises and signs of violence" covering Ms. Ditchfield's body, brain damage, paralysis on the left side of her body and a clot in her right cerebral artery. Notably, the pathologist found none of blood or bone fractures that would characterize a beating brutal enough to cause brain damage.

The cause of death was brain swelling, he concluded, caused by "a blow on the head with a broad, blunt object and delivered at extreme force."

On March 11, 1971, a jury found Mr. Salmon guilty of manslaughter. A judge sentenced him to 10 years in prison.

"It was not a good feeling," says Mr. Salmon today. "I knew I didn't do it. I always figured when I went to court I'd eventually be out."

After his release in 1974, he moved to the Orillia area, knowing his checkered past would prevent any happy future in Woodstock.

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The conviction remained a life-long hindrance, blocking his path to a government job, a position with the local volunteer fire hall, mortgages.

But then two people came into his life who would change everything. In 1979, there was Margaret, a non-drinking registered nurse. "He told me about the conviction right up front," she says. "I knew then this man wouldn't hurt a female. Thirty-five years of marriage later, I'm still right about that."

Around 2000, he read about AIDWYC's fight to overturn the murder conviction of Steven Truscott. He called the lead lawyer, James Lockyer, launching a 15-year bid to overturn his conviction.

About five years before Ms. Ditchfield's death, pathologists refined a method of determining whether a head injury was caused by the skull striking a stationary object – as would be the case in a fall – or an object striking a stationary skull – as would be the case with a punch or kick. The original pathologist had ignored the technique.

Mr. Lockyer seized on the oversight and commissioned three new pathologist reports. They unanimously agreed Ms. Ditchfield's injuries stemmed from a contrecoup contusion. In short, her head hit something, not the other way around.

They found mention of the brain clot especially compelling. The contusions likely had resulted, they found, from a series of falls and attempts by medical staff to place her on a ventilator.

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The new conclusion: A fall triggered a stroke that eventually killed her.

On June 4, the Crown filed a factum conceding the fresh pathology evidence and is recommending an acquittal in the case, scheduled for Monday morning.

When Mr. Lockyer phoned him with the encouraging news, Mr. Salmon celebrated by hugging all five cats.

Some people are less thrilled. "I don't doubt the new evidence," says one family member who did not want to be identified. "But he let her lay there for days. Why didn't he seek help immediately?"

It's one regret that remains with Mr. Salmon. "She hit her head on the tub. That's when, looking back, I should've taken her to the hospital," he says. "But I didn't know nothing about concussions or any of that stuff then."

He only blames the seventies-era justice system.

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"I felt the whole time I'd beat this," he says. "I never lost faith."