MEXICO CITY — The authorities on Wednesday provided a broad account of the apparent abduction of 43 college students last month in southern Mexico, saying that the police in a small city attacked them on orders of the mayor and his wife out of fear they were going to disrupt a speech she was giving.

The police detained the group, students from a left-wing teachers’ college who had angered the mayor during a previous demonstration, Attorney General Jesús Murillo Karam told a news conference. The students, he said, were then turned over to a gang linked to Mayor Jose Luis Abarca of Iguala and his wife, María de los Ángeles Pineda Villa.

The local crime boss, informed by a lieutenant in a text message that the students belonged to a rival gang, apparently ordered their disappearance. Mr. Murillo Karam did not say what happened to them.

The gang leader, Sidronio Casarrubias Salgado of the Guerreros Unidos, “approved the actions to, quote unquote, defend his influence over the territory of Iguala,” Mr. Murillo Karam said. Mr. Casarrubias was arrested last weekend.