MANDEL: Julia MacIsaac’s ex-boyfriend rewarded her compassion by killing her

The medical lab tech allowed David Slinger to live in her Scarborough home long after they broke up, and he beat her to death with a baseball bat

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Published Apr 24, 2026  •  Last updated 6 hours ago  •  3 minute read

Medical lab tech Julia MacIsaac, 42, was beaten to death in her Scarborough home by her ex-boyfriend David Slinger on March 14, 2024. Photo by Supplied by friend

Julia MacIsaac was a gentle and compassionate soul.

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Even though she’d moved on years earlier to a new relationship, she allowed her troubled ex-boyfriend to live in her Scarborough home because he had nowhere else to go.

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But for safety, the medical lab technologist put a lock on her bedroom door. Tragically, it wouldn’t be able to save her.

In a downtown courtroom filled with MacIsaac’s grieving family and friends on Friday, David Slinger admitted he repeatedly banged on her door and forced his way inside in the early hours of March 14, 2024.

David Slinger, now 48, pleaded guilty to second-degree murder in the 2024 killing of his ex-girlfriend Julia MacIsaac on Friday, April 24, 2026. Facebook

Struck her repeatedly with a baseball bat

“The video camera in the stairwell captured audio of Ms. MacIsaac screaming, followed by her voice being muffled and then a series of loud bangs,” says an agreed statement of facts read into court. “During this time, the accused started choking Ms. MacIsaac, then repeatedly struck her with a baseball bat on her body and head.”

The unkempt and overweight former construction worker, now 48, pleaded guilty to second-degree murder, which carries an automatic life sentence. Superior Court Justice Maureen Forestell imposed 12 years of parole ineligibility, a term recommended jointly by the Crown and defence.

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“A weapon was used against an unarmed, defenceless and vulnerable victim. The murder was committed in the home of the victim – a place that should be a place of safety and security,” the judge said. “If not for the mental health issues of Mr. Slinger and the guilty plea in this case, there’s no question that parole ineligibility period would be higher.”

Toronto Police at the scene of a homicide on Scarborough Golf Club Road on Thursday, March 14, 2024. A woman was found dead, a man is in custody. JACK BOLAND/TORONTO SUN

Hoped to be found not criminally responsible

Slinger, it seems, had initially hoped to be found not criminally responsible (NCR) due to a mental condition. When he called 911 shortly after the murder, he said he was in a “psychosis” and had just strangled and beaten his roommate.

However, a forensic psychiatrist hired by the defence said he suffers from bipolar disorder but didn’t meet the stringent criteria for NCR.

Three days before the slaying, Slinger had been discharged from hospital after treatment for suicidal thoughts. MacIsaac, 42, was worried about him returning to her townhouse on Scarborough Golf Club Rd., south of Kingston Rd.

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According to the agreed statement, she told his sister as well as her current partner – she and Slinger had split in 2017 – that she was concerned about his behaviour and was uneasy about him living with her, but he had nowhere to go.

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MacIsaac loyal to a fault

Her older brother, Michael MacIsaac, said she was loyal to a fault.

“I told her to get rid of her anchor but she wouldn’t, telling me this dark soul was her best friend,” her angry brother told the court, refusing to name her killer except as “creature.”

“I knew this anchor was pulling her under but she was a great swimmer. I just didn’t think that it would make her drown.”

What a light he extinguished.

Medical lab tech Julia MacIsaac, 42, was beaten to death in her Scarborough home by her ex-boyfriend David Slinger on March 14, 2024. Instagram

In many emotional victim impact statements, court heard MacIsaac was a vegan, a Buddhist, a “Lord of the Rings” fan and an animal lover who’d rescued two chinchillas. She’d overcome numerous challenges in her life: her father died when she was just 13 and in 2013, she was assaulted by a former boyfriend, which lead to issues with alcohol.

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She overcame it all, earning two post-secondary degrees and establishing a career in microbiology research.

Her older sister Jennie, a touring musician, recalled one of the last gifts MacIsaac gave her was a lock for her hotel room doors.

“She wanted me to be safe. She was thinking about my life, my travels and how to protect me,” Jennie said, fighting back tears.

“I was her older sister,” she wept, “and I could not protect her.”

Medical lab tech Julia MacIsaac, 42, was beaten to death in her Scarborough home by her ex-boyfriend David Slinger on March 14, 2024. Photo by Handout /Toronto Police

Unbearable knowing sister’s life ended so violently

As Slinger listened with his head in his hands, she said it was unbearable to know her sister’s life ended so violently in a place where she should have been safe.

“My thoughts constantly return to Julia – what she must have gone through, the fear she must have felt and her final moments. Those thoughts do not stop. They follow me everywhere.”

The horrible irony, said her brother Matthew MacIsaac, is that Slinger killed the one person who probably cared most about him in the world.

“There’s no just world where given the choice, David is here and Julia isn’t,” he said. “I can’t make this make sense.”

Offered a chance to speak, the coward had nothing to say.

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