03/28/2013 05:31 EDT | Updated 05/28/2013 05:12 EDT

Man found guilty for stabbing common-law wife's lover while the three stargazed

Clive Gibbons met Edna Mueller when they were youngsters in an astronomy club and about 30 years later, he tried to kill her lover with a machete as the three of them were stargazing.

Gibbons was convicted this week in Milton, Ont., of attempted murder for a May 30, 2011, attack on the man his common-law wife had been seeing.

The couple was together for three decades, living together for two of those decades in Burlington, Ont. Gibbons worked as a technician in a university geology department and Mueller was a geophysicist.

But then, Mueller's interest in Napoleonic history led to an affair with Napoleon expert David Markham, according to the tale woven in the court decision.

Gibbons was devastated when Mueller broke the news of the affair to him, but he urged her to stay in their home in the hopes that she would come back to him. He even struck up an apparent friendship with the lover.

"While they socialized, the accused began to ruminate and dwell upon the relationship between Edna and David," Superior Court Judge Katherine M. van Rensburg wrote in her decision.

"He found David's behaviour insulting, but did not express his anger, even after David gave him some 'friendly advice' about his sexual inadequacy."

That is, until the fateful evening, when Gibbons' simmering rage boiled over. Gibbons testified at trial that the "last straw" was when Markham urinated against a tree in Gibbons' backyard.

At first Gibbons and Markham communicated through friendly emails, but they eventually met at a scotch tasting event at Mueller's mother's house, a few weeks before the attack.

Their second meeting came at the end of May 2011, when Markham — who lived in the United States — visited to close on a condo that he and Mueller bought in Toronto.

The three went to an antiques show together then Gibbons invited them over for chili and scotch, van Rensburg wrote. The evening seemed to go well until Markham said he was uncomfortable that Mueller was 15 and Gibbons was 21 when they first started dating.

Markham also made several other remarks to which Gibbons took exception, but he kept his cool, van Rensburg wrote.

A few days later the three went out for dinner, then back to Gibbons' home for stargazing. They took turns looking through the eyepiece, van Rensburg wrote, and at one point when Markham bent over the telescope, Gibbons reached into the nearby shed and grabbed a machete.

He stabbed Markham in the back, then in the neck. Markham needed 19 stitches, most of them to the front of his neck.

Gibbons overdosed on anti-depressants and alcohol, then called a friend and told him he tried to kill Markham. The friend called 911 and Gibbons survived.

Later, police found several letters Gibbons had written, some of which described his plans to kill himself and Markham. One was handwritten and addressed to Mueller, saying "You'll never know how much I loved you, dear."

Gibbons had also addressed a letter to Markham, saying he should have kept his distance.

"Perhaps you thought I was too weak to harm you," the letter said. "Too afraid to hurt Edna's feelings. Not the vengeful type. That I'd roll over and let you have your way. I allowed you to think that, up until now. Our first and last, fateful meeting. It gave me great pleasure to remove you from the face of the Earth. To watch the life drain from your old, pathetic body."

Gibbons tried to argue at trial that the writings about killing Markham were works of fiction, and that he only intended to wound Markham in the machete attack.

But van Rensburg wrote that she had no doubt that Gibbons intended to kill Markham and himself out of "his despair, anger and resentment."