(Reuters) - A Mexican mayor and his wife were "probable masterminds" behind the disappearance of 43 student-teachers last month in the restive southwest, the country's attorney general said on Wednesday. The students went missing on Sept. 26 from Iguala in the southwestern state of Guerrero, after they clashed with police. The incident sent shockwaves across Mexico and undermined President Enrique Pena Nieto's claims that Mexico is getting safer under his watch. So far, federal authorities have arrested 52 people in connection with the incident, including dozens of police who have links to a gang called Guerreros Unidos, or "United Warriors." The gang's leader, Sidronio Casarrubias, was caught last week.