Mexico's general director of airports and auxiliary services says investigators found no mechanical problems or evidence of an explosion.
Gilberto Lopez Meyer says the aircraft was flying through fog in near-zero visibility last November when the pilot changed course and the helicopter crashed into a mountainside south of Mexico City. Meyers said Friday there wouldn't have been an accident without the route change.
The interior secretary is the Mexican government's No. 2 official, and Blake Mora was the second interior secretary under President Felipe Calderon to die in an aircraft crash. Many Mexicans have found it hard to accept as an odd coincidence.