MEXICO CITY: Mexican officials said Friday that they had detained a leader of the group of criminals who prosecutors believe killed 43 college students then burnt their bodies, in a case that continues to roil the country more than three months after the young men disappeared.

The arrest of Felipe Rodriguez Salgado, who was being questioned late Friday, may add more details to the theory authorities have outlined.

Prosecutors say municipal police in the southern city of Iguala, in Guerrero state, had arrested the students and handed them over to the Guerreros Unidos organised crime group on orders from the city’s mayor, Jose Luis Abarca.

Abarca and his wife, Maria de Los Angeles Pineda Villa, are believed to be closely linked to Guerreros Unidos. The pair fled Iguala, then were arrested in Mexico City in November. Authorities formally charged Abarca in the students’ disappearance Tuesday. At the same time, Pineda was charged with involvement in organised crime.

The case, which peeled back the ways in which drug gangs have succeeded in buying off the local police and officials in many parts of the country, has shocked Mexico and challenged President Enrique Nieto’s efforts to focus public attention on the economy.

Turmoil is rising in Guerrero state, where masked protesters have been burning state buildings and cars and disrupting public events.

The families of the missing young men, who were studying to be teachers at the Escuela Normal Rural, have questioned whether the students are dead. The remains of only one of the 43 students have been identified so far by a special laboratory at the University of Innsbruck in Austria. Some of the families began a new search in the hills around Iguala on Friday.

On Monday, some relatives gathered outside the army base in Iguala, demanding to be allowed in to see if their sons were inside. The army said it will allow the National Commission for Human Rights to visit the base with relatives.

Rodriguez, whom officials described as a Guerreros Unidos hit man, is believed to have ordered the group that killed the students and burnt the bodies to remove all traces of the crime. According to the authorities, he took orders from a lieutenant named Gildardo Lopez Astudillo, who is a fugitive.

Officials believe Lopez orchestrated the students’ disappearance in September on orders from the leader of Guerreros Unidos, Sidronio Casarrubias Salgado, who was arrested in October.

Almost 100 people have been detained in the investigation, officials announced this week. The majority of those are police officers from Iguala and the neighbouring town of Cocula, the site of the trash dump where prosecutors say the students were killed and then cremated.