BOSTON (AP) -- 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.