Alejandro Cerezo, a 23-year-old economics and sociology student, was leaving a federal prison on Tuesday, a day after a judge ordered his release. Cerezo’s brothers, who were convicted on the same charges, remain in jail and human-rights workers say the case typifies abuse and inconsistencies in Mexico’s justice system. Depending on who tells it, the Cerezo brothers’ saga features dirty prosecutors, clandestine guerrillas and a trio of social activists with a love of literature and art.