OAKLAND — A jury expert testified Tuesday that publicity ahead of the trial of a former San Francisco Bay Area transit officer accused in a fatal train platform shooting has resulted in an “astronomical” level of public knowledge in the case.

The expert, Craig New, said a recent survey by a California State University, Chico professor found that nearly 97 percent of about 400 potential jurors knew details about the case. Nearly 46 percent of those surveyed in Alameda County believe that the officer — Johannes Mehserle — is “definitely guilty” or “probably guilty,” he said.

“The numbers are off the chart,” said New, who was hired by Mehserle’s defense. He added that 82 percent of those surveyed also feared violence if Mehserle, 27, is acquitted.

Mehserle, who is white, has been charged with killing an unarmed, 22-year-old black man with a gun shot to the torso at a Bay Area Rapid Transit station on New Year’s Day in Oakland.

He has pleaded not guilty. His attorney, Michael Rains, is attempting to have the emotionally charged case moved out of Alameda County, arguing that his client wouldn’t get a fair trial there.

Rains has cited the violent protests in downtown Oakland that followed the shooting. He also has mentioned that two Alameda County judges have said publicly that they do not believe Mehserle’s defense.

New testified that about 80 percent of blacks polled said they think Mehserle is guilty of murdering Oscar Grant, compared with just 33 percent of whites who have the same belief.

Deputy District Attorney David Stein asked New if the wording in one of the survey questions dealing with the fear of violence could skew the results. “It could,” New said.

Rains argues that Mehserle meant to use his Taser to restrain Grant, but accidentally pulled his pistol while Grant was lying face down on the station platform.

The shooting was video-recorded by several bystanders, shown across the Internet and subsequently used as evidence in a preliminary hearing last spring.

New will continue his testimony on Wednesday.