A gag order is issued by a judge, usually in a court case with a great deal of notoriety.

It prohibits the attorneys, witnesses and others involved in the legal proceedings from publicly discussing certain aspects of a case if the judge feels such disclosure would prejudice potential jurors and influence the trial's outcome.

In the case of Johannes Mehserle, the BART officer accused of shooting Oscar Grant III, the gag order itself is jeopardizing the fairness of the trial. Alameda County Superior Judge Morris Jacobson had an opportunity Friday to do the right thing and lift the gag order that he imposed three weeks ago in the People v. Mehserle.

Yet he refused the request by Mehserle's attorney Michael Rains. In doing so, he employed what I believe to be questionable logic.

Jacobson said he feared Rains would use the media to taint the jury pool and create a case for a change of venue.

Beg your pardon judge, but I believe you are attempting to try to shut the barn door after the horse has bolted.

Grant, a 22-year-old Hayward man, had become a cause celebre within mere days of his Jan. 1 killing. Google Oscar Grant III and you'll get more than 8 million hits. There are countless postings of the infamous cell phone videos, which have gone viral. There are Internet sites calling Mehserle a "killer cop." Someone has even named a collard greens recipe in Grant's memory.

There have been a number of news conferences that have all but convicted Mehserle. Every hiccup in the case has been reported by this newspaper and other media.

District Attorney Tom Orloff held a news conference to announce he was charging Mehserle with murder as opposed to the lesser charge of manslaughter.

Standing before television cameras, Orloff said: "I feel that the evidence indicates that this is an unlawful killing done by an intentional act."

At another news conference, attorney John Burris, who is representing Grant's family in a $25 million lawsuit, called the shooting "the most unconscionable" he has ever seen.

City Councilmember Desley Brooks stood in front of City Hall and called the shooting an "execution," the equivalent of yelling "fire" in a crowded movie theater.

Everyone pretty much has said what they have wanted to say except for the one person we all want to hear from: the defendant.

Rains had argued, quite reasonably I believe, that the gag order is preventing the defense from responding to unfavorable allegations about his client in the media. In his request that the gag order be lifted, Rains wrote: "The defense believes that the order has hamstrung Mehserle by preventing any attempt he might otherwise make to address the barrage of negative publicity in the case which has presumed his guilt as a murderer."

Under the order, no one on Mehserle's defense team can talk to the media about Mehserle's character, his credibility, nor any statements he may have made before, during or after the shooting.

Those factors are crucial if we are ever to piece together what led to this tragedy. We deserve to hear, in Mehserle's own words, what prompted him to fire the shot that killed Grant.

In the absence of an explanation, Mehserle is presumed guilty of murder in the court of public opinion. It must be noted, however, that Mehserle didn't help his case by quitting so he wouldn't have to talk to BART investigators.

Jacobson went on to scold Rains for releasing his bail motion document — which, the last time I checked, was a matter of public record.

That document included the names of more than a dozen witnesses who told investigators they overheard Mehserle say he was going to use his Taser on Grant. Some described a shocked expression on Mehserle's face after he fired the fatal shot.

Were it not for the information in that bail document, we would know nothing of Mehserle's possible motive.

True, Mehserle may not be telling the truth when he says he thought Grant was going for a gun. The Taser defense could be bogus. But that's for a jury to decide.

It shouldn't be up to a judge to censor the information that gets released to the public before the trial.

There is absolutely no justification for a police officer to shoot an unarmed man in the back while he is lying facedown on a BART train platform.

If Mehserle is found guilty, he must be punished.

Yet we must guard, carefully, against allowing this tragedy to disintegrate into a witch hunt.

Tammerlin Drummond is a columnist for the Bay Area News Group-East Bay. Her column will run this week in Metro on Wednesday and Friday. Next week it resumes its regular schedule: Wednesday in Metro and Sunday in Opinion. Reach her at tdrummond@bayareanewsgroup.com or on Facebook.