MEXICO CITY - Mexican authorities on Wednesday announced the arrest of an alleged mastermind in the assassination of a popular opposition mayor, a vocal critic of the government's security policies whose murder has shocked the country and sparked mass protests.

Carlos Manzo, the mayor of Uruapan in the major avocado-producing state of Michoacan, was shot and killed during a public Day of the Dead celebration on November 1 while he was with his family. Manzo had repeatedly accused the federal government of failing to act against organized crime.