The defence motion came on the heels of Superior Court Justice Edward Gareau's decision earlier in the day, denying a Crown request that the woman be permitted to give her evidence by closed-circuit television.
It took both Gareau and prosecutor David Kirk by surprise.
The assistant Crown attorney told the court he didn't know about Wilson's intention to seek a mistrial until Gareau came into the courtroom following the lunch break.
Calling it "an unfortunate situation," Willson explained to Gareau he was taking this step "not without a lot of thought and hesitation."
"I have deep concern whether you should continue as trier of fact," he said, adding it had nothing to do with Gareau's decision about the complainant's mode of testimony.
The veteran lawyer said his problem related to information the Crown had provided the court in support of its application.
Willson pointed to a "pretty intricate summary" of a video statement the complainant had given the police.
"What the Crown has done here to support the application is to file a prior consistent statement" which "is inadmissible in this trial," he maintained.
The application should have been heard by another judge, he said. "It's prejudicial."
Marin, 63, has pleaded not guilty to six charges — sexual interference, touching a person under the age of 14 for a sexual purpose, sexual touching and three counts of sexual assault.
The offences are alleged to have begun in the early 2000s and continued to 2015.
A publication ban prohibits reporting any information that could identify the complainant.
On Tuesday, Kirk told the court there is evidence the woman suffers from post traumatic stress disorder and anxiety as a result of sexual abuse.
He said the complainant has a "heightened anxiety" about being in the courtroom with Marin, and suggested "to facilitate a full and candid account" that she be allowed to testify via CCTV.
Willson opposed the application, but indicated he had no problem with woman giving evidence behind a screen in the courtroom.
When he dismissed the application Wednesday, Gareau said if there had been a full medical report from the complainant's doctor, indicating in detail what her condition is and the impact on her of testifying in the courtroom, his decision would be different.
The judge then told Kirk he was going to give him an opportunity to get such a report or the Crown could have her testify with a screen.
He then adjourned court for an hour so that the Crown could speak with the witness.
When the case resumed shortly after 11 a.m., Kirk asked that it be put over until the afternoon so the woman could try to get hold of her doctor.
When court resumed at 2 p.m., the complainant was in the witness box, behind a screen and ready to testify.
It was then Willson asked the judge to consider recusing himself.
He then provided a letter he had sent the Crown on June 6 __ two days after the prosecution had filed its application with the court.
Willson said he had indicated that another judge, other than the trial judge, should hear the application, but he had not received a response.
At that point Gareau questioned why he hadn't objected on Tuesday when the court started to hear the application.
Gareau also noted that such applications are usually heard by the trial judge.
Willson replied that he had the application to answer.
"I felt I had to deal with it in the way I did," he said. "I'm not aware of any response to the letter. I don't know what else I could do."
Gareau said seven days had been scheduled for the trial, the application had been argued "and after not objecting to the application you ask for a mistrial."
"I'm not happy at all about that," he told Willson.
The matter was put over until Thursday to give Kirk time to prepare a response to the defence motion.
Calling it a "serious situation," Gareau said he was "going to consider it carefully."
He indicated he may have a decision on Friday or Monday.
"A mistrial is an extraordinary remedy."
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