A B.C. man found guilty of stabbing his pregnant lover to death has had his murder conviction overturned and will have a new trial.

Amjad Khan and his alleged accomplice Naim Mohammed Saghir were convicted by a jury of killing 21-year-old Tasha Rossette in the threshold of her Surrey apartment in November 2005. She was 17 weeks pregnant with Khan's baby at the time.

During the 2008 trial, two people testified that Khan had tried to hire them to kill Rossette, alleging that he referred to her pregnancy as a "headache" that would bring shame on his family and told them "the only way to get rid of this problem is to kill her."

A B.C. Court of Appeal panel ruled Tuesday that the probation officer of one those "unsavoury witnesses" had given evidence that improperly presented him as truthful and trustworthy.

"The Crown tendered inadmissible oath-helping evidence to support the credibility of one of those witnesses and improperly cross-examined Mr. Khan," Justice David Frankel wrote in the decision overturning Khan and Saghir's first-degree murder convictions.

In Canadian law, unsavoury witnesses can include people living a criminal or amoral lifestyle and those who cannot be trusted to tell the truth.

The three-judge appeal court panel also ruled that the trial judge gave "flawed" directions to the jury about the possibility that someone else had murdered Rossette.

Khan and Rossette had known each other since high school, and were in a "casual sexual relationship" leading up to Rossette's pregnancy according to court documents.

On the day of the murder, Khan picked Rossette up from a friend's house and took her out to a Subway restaurant for dinner. He claimed he dropped her off in the alley by her building and didn't see her alive again.

Rossette's sister discovered the body two days later. She was lying in a pool of blood, her throat slashed and her body stabbed 40 times. A Subway sandwich was lying nearby.

The murdered woman left behind a three-year-old daughter.

One of the "unsavoury witnesses" testified during the original trial that Saghir had told him he'd killed a woman Khan had gotten pregnant. He said Saghir was holding a knife in a plastic bag, and said he had to "slice that bitch's throat because she was fighting back."

Khan's ex-girlfriend testified that Khan told her he had "dealt with" a woman claiming to be pregnant with his child.

However, no forensic evidence was uncovered connecting Khan and Saghir to the killing, and a murder weapon was never found.

During the trial, Khan's lawyers suggested that a woman named Ruby Jubbal, who had paid Rossette to enter a sham marriage for immigration purposes, might have been responsible for the murder.

Defence counsel alleged that Rossette had threatened to report Jubbal to immigration authorities because she was unhappy with the amount she was paid.

Jubbal denied having anything to do with the murder.

A new trial date has yet to be set for Khan and Saghir.