A small medical transport plane crashed and caught fire Tuesday on the Navajo Nation in northern Arizona, killing all four people on board, the tribe said.

Federal investigators on Wednesday were trying to piece together what caused a medical transport plane to crash on the Navajo Nation in northern Arizona, killing the four people on board and leaving the medical community in neighboring New Mexico heartbroken.

Four people were killed after a medical transport plane crashed near Chinle Airport Tuesday. The cause of the crash is unknown.