MEXICO CITY (Reuters) - Mexico wants a full investigation by U.S. authorities on Friday into a shooting on the U.S. border that left three illegal migrants dead and two injured. Mexico's Foreign Ministry said it had told the Mexican consulate in Tucson, Arizona, to ask local U.S. authorities to probe the attack by unknown gunmen, which took place on a back road often used by migrant traffickers. The ministry requested "an exhaustive investigation" into the incident, it said in a statement. Armed men stopped a bus full of people on the remote desert track near Tucson and began shooting at...