The surfers' burnt-out van was found with two unidentified bodies last weekend.
Mexican officials say the suspects confessed to shooting a long-haired tourist in the face when he resisted a robbery on a road in the gang-plagued state of Sinaloa on November 21.
They say the robbers then killed the second man, drove the vehicle to another location and set fire to the van with two bodies inside.
Aussies Dean Lucas and Adam Coleman were last seen in the Sinaloa town of Topolobampo on November 20.
