(Keizer, OR)  --  The Oregon State Medical Examiner's Office says a 12-year-old Keizer boy who was found dead in the apartment he and his mother shared was strangled.  Caden Berry was a seventh-grader at Clagget Creek Middle School.  His mother, 38-year-old Amy Robertson, is charged with aggravated murder and is being held without bail.  Robertson is likely to appear in court today.