OTTAWA -- The Supreme Court of Canada has ruled that just because a killer concealed the body, cleaned up the crime scene and lied to police, the actions do not necessarily prove there was intent to commit murder.

The country's top court upheld an appeal court ruling Friday that overturned the 2011 second-degree murder conviction of Jason Rodgerson in the death of 21-year-old Amber Young in Oshawa, Ont.

A new trial will be held for Rodgerson, who has admitted killed Young in 2008 in 2008 during a drunken, drug-fuelled tryst but claims it was in self defence.

Justice Michael Moldaver, writing the Supreme Court judgment, agreed with an appeal court that the trial judge did not properly instruct the jury on how to weigh the evidence.

"I would dismiss the Crown's appeal and affirm the Court of Appeal's judgment ordering a new trial on a charge of second-degree murder," Moldaver concluded.

The trial judge should not have instructed the jury that Rodgerson's attempt to flee police and his lies after Young's death were evidence of an intent to commit murder, wrote Moldaver, calling it a "legal error (that) amounted to misdirection, not non-direction."

The top court also found that the trial judge's day-long, 200-page charge to the jury was confusing and failed to properly explain how the jurors should assess Rodgerson burying the young mother in a shallow grave in his backyard and using bleach to clean up the crime scene.

"I have concluded that the trial judge erred by failing to sufficiently aid the jury in understanding how to use the evidence of post-offence concealment and clean-up on the issue of intent," wrote Moldaver.

The justice also took the Crown to task for charging Rodgerson with first-degree murder, calling the evidence for such a charge "paper thin."

Evidence showed Rodgerson and Young, who had a young son, first met in a bar in Oshawa on the day she died. After drinking and consuming prescription drugs and ecstasy, they went to Rodgerson's home and had consensual sex twice.

Rodgerson claims Young then attacked him with a knife in a dispute over paying her $5 for the ecstasy, and that he hit her twice.

"This struggle culminated in him pressing down on her face with his forearm until she appeared to pass out," according to the Supreme Court judgment's statement of facts.

Rodgerson awoke the next day to find Young dead in his bed, and panicked because he had a small marijuana grow-op in the basement.

He stripped her and buried her in a metre-deep grave in the home's backyard, then attempted to clean the crime scene. Police arrived a few days later on a tip from his grow-op partner.

"Jason Rodgerson's post-offence conduct is very significant," trial judge Bryan Shaughnessy was quoted in sentencing him to 14 years for second-degree murder.

"His sole concern was hiding the body and removing any evidence of his violent struggle with the young woman."