Mexican authorities have captured the suspected leader of the Guerreros Unidos gang, which was allegedly involved with corrupt police in the disappearance of 43 students, officials announced.

Attorney general Jesus Murillo Karam said on Friday that the arrest of Sidronio Casarrubias would open a "new line of investigation" to find the college students who have been missing for three weeks.

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

Mexico expands search for missing students

He did not say when or where the arrest took place.

Al Jazeera's Rachel Levin, reporting from Mexico City, said that while the arrest is significant, the government's effort to end drug-related violence in the state of Guerrero remains in doubt.

"They are trying to show that they are cracking down," she said. "But cleaning up the government and the system here - that takes a lot longer."

Our correspondent also reported that on Friday, at least 5,000 demonstrators marched in the streets of Acapulco, a major business hub in Guerrero, to demand more action from the government of President Enrique Pena Nieto.

The announcement of the arrest 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 then handed the students to their counterparts in the neighbouring town of Cocula who eventually delivered the 43 young men to the Guerreros Unidos, authorities say.

Source: Al Jazeera and agencies