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Raquenel Villanueva, 55, had survived four previous assassination attempts in the past, including a 1999 attack in Mexico City when she sustained wounds from gunfire.
Villanueva had defended drug lords including regional chief of police Carlos Resendez Bertolucci, who had been sent to jail over his alleged links to drug cartels.
The incident comes ahead of United States president Barack Obama's visit to Mexico to meet local President Felipe Calderon and Canadian Prime Minister Stephen Harper for the trilateral summit in Guadalajara, a meeting aimed at stamping out drug gang-related violence.