The First 48 S08E09 - Out of Sight / Missing Piece

In Minneapolis, after a night out with friends, a college student is stabbed to death while getting on his scooter to ride home. During a canvass of the crime scene, lead investigator Sgt. John Holthusen is confronted with the neighborhood's escalating violence when he catches a man being attacked. Holthusen must determine if the assailant is also the killer.