Mexican authorities have asked U.S. and French aviation crash experts to help investigate the helicopter crash that killed Interior Minister Francisco Blake Mora, a key figure in fighting the country’s illegal drug cartels.

Officials say Mora was killed Friday while traveling between Mexico City and the state of Morelos.

President Felipe Calderon said the helicopter crash happened in foggy conditions and was probably an accident. The president, however, said all possible causes are under investigation. 

Seven other people were on board the helicopter and were also killed.