The Crown prosecutor in Randy Tshilumba's murder trial has suggested that Tshilumba invented a story about fearing for his life and falsified medical documents in order to avoid flunking out of school.

Tshilumba, 21, is charged with first-degree murder in the death of 20-year-old Clémence Beaulieu-Patry.

Tshilumba has admitted to fatally stabbing Beaulieu-Patry while she worked at a Maxi grocery store in Montreal's Saint-Michel neighbourhood in April 2016.

Clemence Beaulieu-Patry

Clémence Beaulieu-Patry was stabbed to death while working at a Maxi supermarket in April 2016 in Montreal's Saint-Michel district. (Facebook)

Tshilumba's lawyer has argued that his client was mentally ill at the time of the killing and didn't believe what he did was wrong.

Crown prosecutor Catherine Perreault began trying to poke holes in that argument as she cross-examined Tshilumba Monday.

Over two and half days of questioning from his own lawyer, Tshilumba suggested that in the months leading up to the killing he became increasingly anxious because he was worried that Beaulieu-Patry, an acquaintance from high school, and a group of her friends might be trying to kill him.

He cited unspecified messages on Facebook, the exact details of which he couldn't recall, but that he believed contained "indirect threats" aimed at him.

He testified he became so anxious and fearful for his life that he consulted two different doctors about it.

Altered doctors'  notes

During cross-examination, Perreault suggested Tshilumba had another reason to consult a doctor.

Perreault noted Tshilumba's grades had been suffering at CEGEP and that he was at risk of failing.

Obtaining a note from a doctor declaring that he was incapacitated and unable to attend school for a period of at least three weeks would enable Tshilumba to avoid flunking out.

His school year would instead be declared "incomplete."

Perreault produced the medical report from the doctor Tshilumba consulted in November 2015.

She noted the date reflecting the period of time Tshilumba had been declared incapacitated had been altered, with someone changing the dates in writing to extend the period of incapacity from one week to three.

Perreault then produced another medical report from a different doctor Tshilumba had seen a year earlier, where exactly the same type of alteration had been made.

Perreault suggested the real reason Tshilumba consulted both these doctors was not because he was suffering from anxiety and feared for his life, but because he was trying to avoid flunking out of school.

"That's false. I had many problems," Tshilumba testified.

"Did you modify these documents?" Perreault asked.

"It's possible, but I don't recall," Tshilumba replied.

"You don't recall if you falsified medical documents two years in a row to avoid failing school?" Perreault asked.

"No," Tshilumba replied.

Never mentioned alleged plot to doctors

Perreault also asked Tshilumba if he had ever spoken to the five young women he believed were conspiring to kill him.

"I never had conversations with them," he replied.

Perreault asked Tshilumba why he never mentioned this alleged plot to kill him to either of his two therapists.

Tshilumba repeated what he told the court earlier — that he believed Beaulieu-Patry and her friends might have been in league with one of his doctors in trying to do him harm.

The cross-examination continues Monday afternoon.