A student charged by police with making threats against a South Portland school and its students was welcomed back to school Monday, according to the principal. Mahoney Middle School Principal Carrie Stilphen in a letter sent to parents Friday said the student is “not a threat” to the school. Two weeks ago, South Portland police charged a 14-year-old student with terrorizing after allegedly making threats directed toward other students. Police said the school took action to prevent the student from returning to the school while police investigated.