A new trial has been ordered for a British Columbia man convicted of first-degree murder in the death of an 18-year-old
girl on Halloween night in 2011.

A panel of B.C. Court of Appeal justices has unanimously agreed that two of five issues raised by Mathew Foerster's lawyers are enough to require a second trial.

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Matthew Foerster was convicted of first-degree murder in the slaying of Taylor Van Diest but a new trial has now been ordered. (CBC)

Foerster, who is now in his 30s, was convicted nearly three years ago in the killing of Taylor Van Diest in Armstrong, B.C.

B.C.'s high court says the original jury should have been told Foerster's disposal of a shoelace and flashlight had no bearing on whether he was guilty of murder or manslaughter.

The Court of Appeal also says the jury was incorrectly instructed on how it could interpret Van Diest's last text message before her death, which said she was "being creeped" as she took a shortcut on her way to a Halloween event.

At trial, Foerster admitted he was responsible for the injuries to Van Diest but contended he was only guilty of manslaughter or second-degree murder.

'Like a nightmare case of déjà vu'

The victim's mother, Marie Van Diest, told CBC News she got a call from a Crown lawyer Tuesday morning informing her of the court's decision.

"I think that it's just pathetic that a judge's instructions can be picked apart like that," Van Diest said.

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Marie Van Diest outside the courthouse in Kelowna awaiting the verdict in Mathew Foerster's 2014 trial. (CBC News)

"It's certainly not a case of any victims having any rights at all. It's just more concrete evidence for us that the accused/convicted have all the rights."

Van Diest said her family thought after Foerster's conviction in 2014 they could move on with their lives.

"It's like a nightmare case of déjà vu. We are back at square one," she said.

"Just when you think that your life can carry on and create new better memories, it all just comes flooding back again. [We're] having to brace ourselves to go through it yet again."

Van Diest said she will attend Foerster's new trial and will fight to have the proceedings held in Kelowna again.

With files from Brady Strachan and the Canadian Press.