The alleged leader of a drug gang implicated in the disappearance of 43 college students committed suicide during a confrontation with Mexican forces, a day after protesters demanding an investigation into the students' whereabouts burned government buildings in the southern state of Guerrero.

Federal forces, which include federal police and military personnel, were carrying out an operation to capture Benjamin Mondragon, or "Benjamon," the alleged head of the Guerreros Unidos gang in the neighboring state of Morelos, when a gunfight broke out, according to a federal official who was not authorized to be quoted by name. The official, who spoke Tuesday, did not say which federal force had taken part in the confrontation.

Mondragon killed himself as he was about to be arrested, the official said, though he had no details on how.

The official said it was unclear whether Mondragon had been involved in the students' disappearances.

Guerreros Unidos allegedly had ties to the family of the mayor of Iguala, the city in Guerrero where the students disappeared on Sept. 26 after a confrontation. Police in Iguala killed six people and carried off many of the students before reportedly turning them over to gunmen working for the gang.

Investigators are conducting tests on 28 sets of human remains found at five mass graves outside of Iguala to determine whether they are the bodies of the missing students. Police also have found four other burial pits at a different site, but have not said how many bodies were recovered there.

On Tuesday, Guerrero Gov. Angel Aguirre said many of the bodies appeared to have been in the graves for some time, suggesting they belonged not to the students but to earlier victims of criminal gangs operating in the region.

"Some of these graves were not recently dug," Aguirre told MVS radio. "Some of them are not recent, some are from months ago," he said. Some of the bodies had been burned, making identification harder.

At least one detained gang member has said another Guerreros Unidos leader known as "El Chucky" had ordered him to kill 17 students.

Twenty-six local officers have been detained. Police are looking for the mayor of Iguala, Jose Luis Abarca, in order to question him. His wife's brothers include two deceased top-level members of the gang, which split off from the Beltran Leyva cartel.

The gang controlled drug routes in Guerrero and Morelos.

On Tuesday, protesting teachers sprayed graffiti in support of the missing on bank buildings, a day after hundreds of students and teachers smashed windows at the Guerrero state capital building complex in Chilpancingo, 132 miles (212 kilometers) south of Mexico City, and set fire to some of the buildings.

Students from the school and local teachers blockaded the capital complex, pelting it with sticks, rocks and Molotov cocktails. The protesters are calling for the missing students to be returned alive, even though fears have grown that the mass graves could contain their bodies.

The finance secretary of Guerrero state said six buildings were affected.

Monday's protests came after police shot and wounded a German university student who had been traveling in a van with other students as they passed through Chilpancingo on their way back from Acapulco.

Kim Fritz Kaiser, an exchange student at Mexico City campus of the Monterrey Institute of Technology, was not seriously wounded and was in good condition Monday at a hospital, the institute's director, Pedro Grassa, told Milenio television.

The shooting happened shortly after a police officer had been killed in a confrontation between officers and kidnappers.

Police tried to stop the van, believing it was suspicious, and opened fire when they heard something that sounded like a shot or detonation, said Victor Leon Maldonado of the Guerrero state prosecutor's office. The students kept driving, fearing that armed men might be trying to kidnap them, state prosecutor Inaky Blanco said.

The police involved have been detained and their weapons were being tested, according to the state attorney general's office.

A U.S. State Department travel warning issued last week said U.S. citizens should avoid Chilpancingo along with all parts of Guerrero state outside of the tourist destinations of Acapulco, Ixtapa, Zihuatanejo, Taxco and the Cacahuamilpa caves.

A previous warning in January already advised against travel in the northwestern part of the state near the border with Mexico state, where Iguala is located.