As a former Massachusetts police chief heads to trial on manslaughter charges in the accidental shooting death of an 8-year-old boy at a gun fair, prosecutors and defense attorneys are wrangling over a horrific piece of evidence: a videotape of the shooting taken by the boy's father.

Former Pelham police Chief Edward Fleury is scheduled to go on trial next week in the 2008 death of Christopher Bizilj of Ashford, Conn. The boy was killed when he lost control of an Uzi at a gun fair and shot himself in the head.

Fleury's attorneys say the videotape is gruesome and is likely to elicit an emotional reaction from jurors and prejudice them against their client. They are asking the judge to keep the videotape out of the trial or, if not, then to bar prosecutors from playing the audio portion of the tape, which includes the father's anguished reaction to the death of his son.

Dr. Charles Bizilj brought his two sons to an annual gun show at the Westfield Sportsman's Club on Oct. 26, 2008, and was standing nearby as Christopher fired a 9mm micro Uzi submachine gun at a pumpkin. The boy lost control of the gun as it recoiled.

One of Fleury's lawyer, Rosemary Curran Scapicchio, said the videotape is graphic and could evoke bias against her client. Fleury, who owned the company that organized the event, has pleaded not guilty.

"I'd hate to have the jurors not be able to remain impartial after they've seen the video," Scapicchio said.

The defense also has taken the unusual step of asking Judge Peter Velis to consider showing the video to potential jurors and giving them the chance to decline to sit on the jury if they believe the video is so wrenching that they cannot serve.

"If they know they don't want to view it and they can't handle it, they shouldn't have to, and then they shouldn't sit on the jury," Scapicchio said.

Hampden District Attorney William Bennett did not return a call seeking comment on the video.

Previously, it had been widely reported that Charles Bizilj had been reaching for a camera when his son accidentally shot himself.

Edward P. Ryan Jr., a defense lawyer and former president of the Massachusetts Bar Association, said the judge will have to weigh whether the videotape helps to prove a fact or issue in the case against whether it is unduly prejudicial to Fleury to have jurors watch it.

"Ultimately, I think the judge will let it in," said Ryan, who is not involved in the case.

"It depicts the gun in operation. It could help the jury make a determination as to whether or not allowing the boy to fire the weapon is wanton or reckless," he said. "They get to see the circumstances under which the gun was fired."