Law enforcement officials in Bucks County say it was a credible threat that closed Council Rock South High School on Friday.   Police took a Richboro teenager into custody after searching his bedroom and finding two semi-automatic handguns on a nightstand.   His mother,
50-year-old-Lizabeth Donohoe, was arrested for allegedly making the firearms accessible.   The father of the boy, 48-year-old Vincent Russo of Feasterville, was also arrested for interfering with police.   The investigation started after a student at Council Rock reported the teenage suspect had threatened to shoot up the school.