MURRYSVILLE —Twenty students were injured — four seriously — in a multiple-stabbing incident this morning inside Franklin Regional High School in Murrysville.

Westmoreland County public safety spokesman Dan Stevens said a suspect, also a student, is in custody and was being questioned by Murrysville police and Westmoreland County detectives.

Those seriously injured were flown to hospitals by medical helicopter. Some of the 20 injured students suffered stab wounds to the extremities, he said.

None of the injuries was life-threatening, he said.

The injured students' ages range from 14 to 17.

Just before 7:15 a.m., a school resource officer asked for medical assistance at the school for a stabbing. The students were injured in several classrooms and in the hallways before the classes started, Stevens said.

Parents of the injured students were being contacted.

Police, emergency crews and school buses lined the entrance to the school this morning. A stretcher was loaded into an ambulance around 8:15 a.m.

PITTSBURGH — A woman who pleaded guilty to leaving her 3-year-old twins unattended before a fire killed them has been sentenced to three to six years in prison.Dalawna Berran-Lett, 33, of North Braddock pleaded guilty in December to involuntary manslaughter and child endangerment from the Jan. 4 fire.Police said the boys turned on a burner on a grease-covered stove, sparking flames that soon engulfed the house. Investigators said the boys had previously almost started a fire the previous December when they tried to cook ribs while they were also left alone.Authorities said the defendant, who was sentenced Monday, told them she had left the house in search of stolen marijuana.