Many municipalities have their own police departments, as do many Massachusetts colleges and universities. Massachusetts State Police have sole authority under state law for investigating homicides, except for Boston, Worcester, and Springfield. Fire protection is generally also provided by municipal fire departments but may be divided among multiple smaller departments servicing just individual villages and population centers. Examples of multiple departments servicing the same towns include Dartmouth(three districts) and Barnstable(five districts, plus an airport department). Massport has its own fire department, and its Fire Rescue provides protection on agency property. Fire departments have mutual aid agreements, such as the Massachusetts Metro Fire District in Greater Boston, which facilitate emergency response across department boundaries.