VANCOUVER, B.C. - It's now up to Canada's top court to decide whether Kelly Ellard should face a fourth trial or stand convicted of murder in the vicious killing of B.C. teenager Reena Virk.

All nine Supreme Court of Canada judges heard arguments in the case Monday and reserved judgment. A ruling is not likely for several months.

Virk was 14 years old when she was swarmed by eight teens, beaten and drowned in Victoria in 1997.

Kelly Ellard, 15 when Virk died, was convicted of second-degree murder in 2000 but the decision was set aside on appeal and a new trial ordered.

A second trial in 2004 ended in a hung jury, and a third ended in 2005 with another murder conviction.

That result was once again overturned when a majority of appeals court judges said the trial judge did not properly instruct the jury.

Ellard's defence lawyer tried to convince the top court Monday that her conviction was properly overturned because the judge failed to thoroughly guide jurors on a key point of witness testimony.

Prosecutors countered that any errors were of such insignificance that the conviction should be restored.

At issue is testimony from Marissa Bowles, a teen who witnessed the swarming of Virk by seven young women and one 16-year-old boy. She was not accused of taking part.

Bowles testified at Ellard's third trial that she saw Virk walk across a bridge after the initial beating, followed soon after by Ellard and Warren Glowatski who was convicted in 1999 of second-degree murder in Virk's death.

Glowatski was sentenced to life in prison with no parole eligibility for seven years and has since been released on parole.

A majority of the B.C. Court of Appeal pointed out that what Bowles said in court was different from the sworn statement she gave police 10 days after Virk's death on Nov. 14, 1997. At the time, she did not mention seeing Virk cross the bridge nor did she refer to Ellard or Glowatski following her.

Ellard's defence team now says the jury should have been specifically instructed that any reference to Bowles by the prosecution as a consistent witness on that key detail must be offset by her initial failure to mention it to police.

Ellard, now 26, has been behind bars for almost seven years awaiting a final outcome of the case. She was denied bail pending the Supreme Court hearing.