CHICAGO (CBS) — Chicago Police Officer Jason Van Dyke’s attorney told a judge Friday that too many people in Cook County have formed opinions about his client’s guilt or innocence for Van Dyke to get a fair trial in Cook County in the murder of Laquan McDonald.

Judge Vincent Gaughan has set a Sept. 5 trial date for Van Dyke, and defense attorney Daniel Herbert has filed a motion seeking a change of venue. Van Dyke is charged with first-degree murder in the October 2014 shooting death of McDonald.

In arguing his case Friday morning, Herbert said, after extensive polling, a defense expert found 87 percent of people in Cook County have an opinion in the case, and 74 percent of those polled believe Van Dyke is guilty.

Herbert also said his expert found 67 percent of those polled in Cook County said it would be difficult for Van Dyke to prove is innocence.

“As this court knows, we don’t have to prove anything, but in a case like this, with a Cook County jury, the burden is on the defendant,” he said.

Defense expert Dr. Bryan Edelman testified people in Cook County have more than just a passing awareness of the case, but know specific details of the case, including information that likely would be inadmissible at trial.

“People have developed well-informed opinions about the guilt or innocence of the defendant,” Edelman said. “Presumption of innocence has been undermined.”

Special prosecutor Joseph McMahon countered that the defense’s polling was “manipulated,” and said some of Edelman’s questions were suggestive.

According to McMahon, a prosecution expert found as many as 3.4 million people in Cook County could serve as unbiased jurors, because they either have never heard of the case, or because they would be able to reach a verdict based only on the evidence presented at trial and the judge’s instructions. Even under conditions most favorable to Van Dyke, McMahon said there would be as many as 830,000 people in Cook County who could be fair and unbiased — a larger jury pool than would be available in any other county in Illinois.

However, Herbert said Cook County’s size is not a good enough reason to keep the case here. He said, because of how well-known the case is in Cook County, jurors who live here could face the possibility of being ostracized or threatened if they find Van Dyke not guilty.

Friday’s hearing could last several hours, and it’s unclear if Gaughan is prepared to rule Friday, or if he will rule at a later date.

Van Dyke was charged with murder in November 2015, more than a year after he shot and killed McDonald on the street near 41st and Pulaski.

The officer has said he shot McDonald 16 times because the 17-year-old lunged at him with a knife. However, police dashboard camera video of the incident shows McDonald walking away from Van Dyke when the officer shot him.

Outrage over the video sparked protests in Chicago and around the country.

Van Dyke’s defense team has argued the publicity of the case means the officer can’t get a fair trial in Cook County. They also wanted a different judge to rule on their request for a change of venue, arguing Gaughan is prejudiced, and has already decided not to move the trial.

However, Presiding criminal division Judge LeRoy Martin Jr. ruled Tuesday that state law doesn’t allow for a different judge to rule on only one specific pretrial issue in a case. He also ruled the defense had not shown proof Gaughan is biased.

Gaughan has scheduled a hearing for 9 a.m. Friday on the defense request for a change of venue. It’s unclear if he will issue a ruling at the end of the hearing, or at another date.

It’s also possible, if Gaughan grants the change of venue, the trial would still be held at the Leighton Criminal Courthouse in Chicago. In that case, the judge could have jurors from another county brought in to Chicago to decide the case.

Mike Puccinelli