Last modified: Friday, May 23, 2008 1:24 AM EDT Condition of boy in crash upgraded ATTLEBORO - The condition of a 16-year-old South Attleboro boy critically injured in a car crash last weekend has been upgraded. Nathan Birch, an Attleboro High School freshman hospitalized at Rhode Island Hospital in Providence, was upgraded from critical to serious condition, a hospital spokeswoman said Wednesday. Birch was injured and 17-year-old Attleboro High School junior Rebeckha Whitefield was killed when the sport utility vehicle they were riding in crashed into a tree on Oakhill Avenue. Both were thrown from the vehicle, police and fire officials said. The accident remains under investigation by local and state police assigned to the Bristol County District Attorney's Office. Few details of the investigation have been released.