I spoke with Northfield Deputy Police Chief Chuck Walerius this morning. He said it was a helicopter equipped with a FLIR (Forward Looking Infrared) unit from the Minnesota State Patrol Flight Section. They had requested it to help look for a suicidal individual. The individual was eventually found using cell phone triangulation at around 4:30 am. and was rushed to Northfield Hospital in time.
See the March Strib story titled Thermal imaging: An eye in Minnesota’s sky.