Social media derailed a high-profile murder trial in Moncton today, before it even began.

A judge presiding over the trial of 33-year-old Fred Prosser, who is accused in the death of 25-year-old Sabrina Patterson, declared a mistrial just as the prosecution was about to begin presenting its case this morning in a Moncton courtroom.

A juror was deemed to be potentially biased after it was discovered she made comments on an anti-Prosser Facebook page, forcing the judge to dismiss the entire jury.

Seven men and five women, along with two alternates, were selected yesterday out of a pool of 300 potential jurors to hear evidence in the murder and sexual assault case.

Patterson’s family has been waiting almost two years for the trial to begin and now they will have to wait even longer.

“It’s better to have it happen now, than chances for an appeal or maybe a mistrial halfway through,” says Dale Patterson, the victim’s brother.

It was Dale Patterson who informed the Crown that the juror had made comments on the anti-Prosser Facebook page, which has since been removed from the popular social media site.

The Crown agreed with the defence and Judge George Rideout that the juror’s presence among the other 11 jurors may have created a bias, resulting in a mistrial.  

“The impartiality of the jury is so important in our justice system,” says Crown prosecutor Annie St. Jacques. “We cannot take any chance and have a bad verdict because somebody would contaminate others, so we agree with Justice Rideout.”

Crown Prosecutor Marc Savoie says this is the first time he recalls a jury being scrapped because of comments made online. He also says a closer screening process is needed so it doesn’t happen again.

“I think we need to increase that, just to make sure people really understand that information posts on social media can have an effect on the partiality of a juror,” says Savoie.

The mistrial comes just a day after the jury was selected and after Prosser, a native of Shenstone, N.B., pleaded not guilty to first-degree murder, sexual assault and sexual assault causing bodily harm.

Patterson disappeared in October of 2010 and her body was found in a wooded area of Shenstone nearly two weeks after she was reported missing.

The Riverview woman was Prosser’s former girlfriend, as well as the mother of his two children and the case has received a lot of attention in the community.

Patterson’s sister says the juror should have realized her Facebook comments would be an issue in the trial.

“My understanding is they’re asked if they’ve made any comments in the past, and if they have, that should have been brought forward in the first place,” says Denise Murphy. “We wouldn’t have had to call a mistrial.”

A new trial date has been set for Nov. 20 and a new jury consisting of 12 jurors and two alternates need to be selected.

The process will again take place at the Moncton Coliseum.

With files from CTV Atlantic's Jonathan MacInnis