Jacinthe Prévost is one of a handful of professionals in Quebec with an expertise in blood splatters, DNA, and crime scene investigation, according to criminal lawyers. “I have a murder trial where she’s an expert so I am really happy to have read this decision,” said Mia Manocchio, a Sherbrooke criminal lawyer. “Her credibility will always be questioned following this decision because defence lawyers are always going to use it.”

Khalid Gakmakge was convicted by a jury in the stabbing death of his estranged wife, Lucia Medeiros, in 2009 and was sentenced to life imprisonment with no chance of parole before serving 14 years. The circumstances leading to the death of his wife are relatively clear, points out the appeal court. Gakmakge admitted killing his wife after stabbing her with a large kitchen knife but claimed he did it in self-defence after she first assaulted him with the same knife as he lay in bed sleeping. The Crown asserted that after he murdered his wife, he inflicted stab wounds on himself in an attempt to commit suicide.

The core issue of the trial then was who stabbed who first, and which of the two spouses was the last to be stabbed. During testimony at the preliminary inquiry and in her preparation to testify at trial with a police investigator shortly prior to trial, Prévost said she was unable to answer the question who was the last to be stabbed. “The sequence cannot be given by simply looking at what’s on the blade,” testified Prévost at the preliminary inquiry. But at trial, Prévost had a change of heart after she had “prepared herself more” and entertained “a strong hunch.” During cross-examination, she came to the conclusion that Gakmakge was stabbed last because the majority of the blood found on the knife came from him, a conclusion she never shared with either Crown counsel or the police investigators. “An expert has an obligation to tell the Crown if his testimony will change the nature of his report in order for the defence to be able to present a full and complete defence,” pointed out Manocchio.

Gakmakge argued before the trial judge that if his counsel had known what the expert witness was going to say at trial about the sequence of events, he would have sought to obtain and introduce a contrary opinion. Gakmakge added that if he was not given that opportunity, he would be deprived of a full and complete defence. But the trial judge dismissed his objections in a succinct oral ruling. The trial judge held that Prévost’s testimony was not a “180 degree turn” and that “an expert witness cannot be bound by the exact same answers on a given subject time after time.” He also noted that the trial was well underway and that 14 witnesses had already been heard.

In his appeal, Gakmakge argued that he should have been given sufficient time to hire an expert, at a minimum to assist him in cross-examining Prévost, and at best to prepare a contrary opinion. He also argued once again that he was denied a full and complete defence. The appeal court agreed. “What was at stake here was much more than a mere issue of the jury assessing the credibility of Ms. Prévost’s previous testimony at the preliminary inquiry and comparing it to her different testimony at trial,” said the appeal court. “This is a significant change that can be properly characterized, to use the judge’s words, as a ‘180 degree turn.’ As the appellant argues, it was fundamental for the defence to know what case it had to meet.”

The appeal court also said that Gakmakge should have been given sufficient time to hire an expert, at a minimum to assist him in cross-examining the expert, and at best to prepare a contrary opinion. That option would have been available at a trial by judge alone, which can be adjourned for an extended period of time. But given the impossibility of adjourning the jury trial for the time that would have been required, the “appellant’s subsidiary conclusion” to have the trial judge order a mistrial should have been granted.

That was not the only faux-pas committed by Prévost. The appeal court castigated her for changing her mind on another subject that “fitted nicely” with what she had told the jury about the sequence of events. During cross-examination at the preliminary inquiry she testified that the source of the blood came from both the appellant and his wife. At trial, however, she testified that the only source of the stain was Medeiros’, even though there was evidence of blood cells from Gakmakge. On top of that, Prévost discussed her new conclusions with a workplace colleague during a recess of the trial when she was already in the midst of testifying.

“That was extremely harmful to the defence, and the appeal court was right to order a new trial because the accused was deprived of a full and complete defence,” said Joëlle Roy, the former president of the Quebec Association of Defence Lawyers.

The ruling does not imply that an expert cannot change their opinion, said Véronique Robert, a Montreal criminal lawyer. An expert can make changes to their report but risks losing credibility. “The sciences are rarely exact,” said Robert. “An expert might learn new elements and bring about nuances to his conclusions, but if he changes his opinion he risks losing his credibility.”

Ever since the notorious case of Guy Turcotte, the former cardiologist who was found in 2011 criminally not responsible of killing his two children to death by reason of mental illness, expert witnesses have been under intense scrutiny, noted Manocchio. “They are being watched and have to be very careful about what they say. This decision is a message to them.”