The Supreme Court ruled Tuesday that police do not violate the rights of criminal defendants when, through negligence, they fail to preserve vital evidence or to conduct state-of-the-art laboratory tests. The justices, voting 6-3, reinstated the conviction of an Arizona man in the kidnapping and sodomizing of a 10-year-old boy. A lower court had thrown out the conviction and 10-year prison sentence of Larry Youngblood because police didn't properly preserve semen samples from the child's body and clothing.