Former world champion boxer Juan Jose Estrada was stabbed to death over the weekend in what was believed to be a family quarrel in the Mexican border city of Tijuana, authorities said Monday. Estrada, nicknamed "Dinamita," won the WBC International world championship in the super bantamweight division in 1987, and the WBA title in 1988. Sources close to the investigation said Estrada was taken to a pharmacy early Sunday with a stab wound, but died before an ambulance arrived to take him to the hospital.