The Ontario trucker accused of killing Cindy Gladue will face a new trial for manslaughter, reviving a case that unleashed public outrage over how the Indigenous victim was treated by Canada's criminal justice system.

The Supreme Court of Canada was unanimous Friday in ordering a new trial for Bradley Barton, but justices were split 4-3 on whether he should face trial for manslaughter or first degree murder.

The court found that the justice system failed to protect Gladue and that so-called "rape shield" laws were not followed during Barton's trial, when the jury heard evidence of Gladue's past sexual activities before holding a separate hearing.

Gladue was found dead in the bathtub of a motel bathroom in Edmonton eight years ago, after engaging in paid sex with Barton for two consecutive nights. She bled to death from an 11-centimetre wound to her vaginal wall.

The Crown had argued the wound was caused by a sharp object, but no weapon was ever found.

Barton insisted the sex, which included inserting his fist into Gladue's vagina, was rough but consensual.

Cindy Gladue, 36, was found dead in the bathtub of an Edmonton motel room on June 22, 2011. (Facebook)

Justice Michael Moldaver, writing for the majority, said judges must do more to fight stereotypes against Indigenous victims of violence.

"As an additional safeguard going forward, in sexual assault cases where the complainant is an Indigenous woman or girl, trial judges would be well advised to provide an express instruction aimed at countering prejudice against Indigenous women and girls," he wrote.

Barton was acquitted of first degree murder and manslaughter in 2015, but that decision was later overturned by the Alberta Court of Appeal.

A woman protests outside the Supreme Court of Canada as justices hear arguments in the case of Bradley Barton, who was acquitted of killing Cindy Gladue. (Christina Romualdo/CBC)

'Her life mattered. She was valued'

Moldaver said the justice system failed Gladue and wrote that all individuals deserve to be treated with dignity, humanity and respect.

"Her life mattered. She was valued. She was important. She was loved. Her status as an Indigenous woman who performed sex work did not change any of that in the slightest," he wrote.

"But as these reasons show, the criminal justice system did not deliver on its promise to afford her the law's full protection, and as a result, it let her down — Indeed, it let us all down."

At trial, Barton argued that he had an "honest but mistaken" belief that Gladue had consented to the sexual activity, which involved inserting his fist in her vagina.

The Supreme Court found the judge also erred in failing to "inoculate the jury against mistake of law masquerading as mistakes of fact."

In the dissenting opinion which said Barton should face trial for first-degree murder, Justices Rosalie Abella and Andromache Karakatsanis said the failure to filter Gladue's sexual history without any warning to the jury left the jury with an unchallenged version of Barton's interactions with the deceased.

"This was the narrative's frame in which the victim's conduct was portrayed and the accused's credibility was assessed, creating an image of the deceased that was unfair and would have permeated the whole trial and the jury's deliberations on both murder and manslaughter," the decision reads.

Qajaq Robinson is a commissioner for the National Inquiry Into Murdered and Missing Indigenous Women and Girls, which intervened in the case. She called today's developments at the Supreme Court a "tremendous step forward."

"I think it's a step forward that the court has recognized that in cases of sexual assault against Indigenous women and girls, that there's an obligation on courts, on judges, to be gatekeepers, to ensure that bias, prejudice, racism and sexism do not form part of the evidence, are not what juries and judges rely on to make their decisions," she said.

Sexual past deemed relevant in trial

Section 276 of the Criminal Code, known as the "rape shield law," prohibits the admission of evidence about a victim's sexual activity that could suggest the victim was more likely to have given consent, or was less worthy of being believed.

During the Supreme Court's Oct. 11, 2018 hearing on the case, justices posed tough questions about why details of Gladue's sexual past were openly disclosed and deemed relevant in Barton's trial.

Barton's lawyer Dino Bottos told CBC News the defence only presented previous sexual history because the Crown mentioned it in the opening minutes of the trial. He said the evidence also was germane to the case.

"If she consented to the sexual activity on the first night, the same as the second night, Mr. Barton would have a more reasonable belief that she was consenting to the same sexual activity on the second night," he said.

Case highlights social issues

Bottos conceded the case is "tragic" and highlights important social issues.

He said it also presented fundamental questions about the appeals process that overturned Barton's acquittal. Bottos argued the court of appeal erred in allowing the Crown to use its right of appeal to secure a re-trial based on new theories and legal arguments that were contrary to positions the Crown took at trial.

He said Friday the Supreme Court upheld those grounds of appeal.

"We're pretty happy with that, because if the Supreme Court did not correct that, this would have been a serious change in the way acquittals are handled by courts of appeal," he said.

A new trial for Barton has already been set for February 2020.

"It's a new trial for manslaughter. That's a big difference from a new trial for murder in the first degree," Bottos said. "We certainly didn't want a new trial on anything, but this is, in large measure, a victory for Mr. Barton."

Bottos said his client was acquitted of manslaughter the first time around, and he's "equally optimistic" about the same outcome the second time around.

There were 17 intervenors in the case. Many of them argued that Gladue's death is a symbol of the poverty, abuse and lack of dignity suffered by Indigenous women.

During the trial, Gladue was described repeatedly as "native" and a "prostitute."

After the verdict in the original trial, rallies from St. John's to Victoria took place denouncing the criminal justice system's treatment of the 36-year-old Indigenous mother of three children.

'A horror show'

There was much public outrage over the fact Gladue's vaginal tissue was presented as evidence, in what was believed to be a first in Canada.

Indigenous rights lawyer Jean Teillet said she was disappointed the Supreme Court did not make reference to that act that provoked marches and rallies in the streets in protest.

"That is very disturbing. It allows the criminal justice system to continue to use Indigenous women's body parts as evidence, it allows the state to continue to cut up women's bodies and serve them up on a platter that somebody calls justice," she said.

Teillet said that while it's good that Barton will face a new trial, it will mean more anguish for Gladue's family.

"It was a horror show the first time. It will be worse," she said.

University of British Columbia law professor Janine Benedet, who represented the Vancouver Rape Relief Society at the Supreme Court hearing, said the case underscores how Indigenous women are often the victims of the most brutal forms of gender-based violence. It's also a stark demonstration of how dangerous prostitution can be, she said.

"This case shows you exactly what would happen if the purchase of sex was decriminalized, and how the failure of the police to enforce those laws allows people like Barton to operate with impunity until somebody dies and then they have to take notice," she said.

During the Supreme Court hearing, lawyers for the Alberta government argued the trial judge made several errors and omissions in his charge to the jury regarding absence of motive, the accused's conduct after the act and what constitutes consent.

Today, the Alberta Crown issued a brief statement thanking the Supreme Court for considering the matter.

"Our thoughts remain with the family and friends of Ms. Gladue," the statement reads.