Attorney's General office's special agents custody some of the 27 municipal policemen involved in an attack against students in Iguala last month and now presented to the press in Mexico City

 AFP/ Mexico City

Mexican authorities announced Friday the arrest of the "maximum leader" of a drug gang accused of colluding with crooked police in the disappearance of 43 college students.

Attorney General Jesus Murillo Karam said the arrest of Guerreros Unidos kingpin Sidronio Casarrubias would open a "new line of investigation that can quickly and more easily get us closer to the truth" in the case.

The announcement came hours after thousands of protesters marched in Acapulco to demand the safe return of the 43 young men, who went missing in the southern state of Guerrero three weeks ago.

Tomas Zeron, director of investigations in the prosecutor's office, said Casarrubias was the "maximum leader" of the gang based in the southern state of Guerrero and was arrested alongside "one of his closest operators."

Friday's announcement came three days after authorities said that another Guerreros Unidos leader, Benjamin Mondragon, killed himself when federal police surrounded him in the central state of Morelos.

Authorities say the Guerreros Unidos worked hand-in-hand with corrupt municipal officers in a night of violence in the city of Iguala on September 26 that left six people dead and the 43 aspiring teachers missing.

Iguala's officers shot at the students' buses and then handed them to their counterparts in the neighboring town of Cocula, who delivered the 43 young men to the Guerreros Unidos, authorities say.

Murillo Karam said a total of 36 municipal officers have been arrested in the case.

The attorney general said investigators are still analyzing the contents of three more mass graves found near Iguala after declaring last week that 28 bodies in one pit did not belong to the students.

The mass disappearance has sparked international and national outrage, with protests held across Mexico last week and a new demonstration in the Pacific resort of Acapulco on Friday.

Chanting "they took them alive, we want them back alive," thousands of students, teachers and machete-wielding farmers also called for the resignation of Guerrero Governor Angel Aguirre over his handling of the case.

"We are angry because this is not an isolated event. Many of us are parents and we see very ugly things in this country that we want to fight," said Magdalena Catalan, a 34-year-old teacher.

Many of the protesters wore masks in the latest demonstration over the mass disappearance, which has caused national and international outrage.

More than 1,200 security forces are looking for the college students around Iguala.