At 1727 central time, a Cessna 172 and a Piper PA-28-181 collided in mid-air near Lake Elmo. The flight instructor in the Cessna was killed and the student pilot received serious injuries. The pilot and passenger in the Piper were killed. The Cessna had departed the Downtown St. Paul Airport on an instructional flight and was en route to Lake Elmo Airport. The Piper departed the South St. Paul Municipal Airport and was en route to Silver Bay, Minnesota.