It was news that gave parents hope: None of the bodies found in five mass graves in southern Mexico belonged to 43 teachers college students who have been missing for nearly three weeks since a clash with police.

Mexican authorities made the announcement Tuesday, while also revealing 14 more arrests in the disappearance of the young people, which prosecutors blame on Mexican police allegedly working with a local drug cartel.

"There's a light of hope that they're still alive," said Clemente Rodriguez Moreno, whose 19-year-old son, Cristian Alfonso Rodriguez, went missing after just enrolling in the Raul Isidro Burgos School in the Ayotzinapa area of Tixtla, a town in the southern state of Guerrero.

Forensic investigators are continuing to test other remains and officials have discovered a 10th mass grave, Attorney General Jesus Murillo Karam said at a news briefing.

The 14 arrested police officers confessed to participating in the disappearance, Murillo Karam said. That brought the number of detainees to 50, most of them officers.

The latest are police in Cocula, a town neighboring Iguala, the city where the confrontation took place. Both the mayor and police chief of Iguala are fugitives and accused of links to the local drug cartel, Guerrero Unidos, which is believed to have worked with police in disappearing the students. The gang controls drug routes in Guerrero and Morelos states.

Murillo Karam said that officials had yet to identify the masterminds or a motive in the attack, but that the collusion might have gone beyond just one town.

"There's a connection. We will determine if it was coordination or subordination, but it's clear to me that they were working together," he said of police and drug traffickers in the area.

An alleged leader of the Guerreros Unidos killed himself after being cornered by security forces who were trying to capture him Tuesday, National Security Commissioner Monte Alejandro Rubido said. The official said he had no details on how Benjamin Mondragon, or "Benjamon," killed himself.

Rubido said it was unclear whether Mondragon was involved in the students' disappearance in Iguala.

Police opened fire on about 100 students who had hijacked buses to return to campus after arriving in Iguala to pass the hat for their school. Teachers college students are known throughout Mexico for using radical tactics to raise money and spread their leftist philosophy.

Six people were killed, 25 wounded and dozens of students rounded up by police. There has been no sign of the missing in nearly three weeks, leading investigators to comb for clandestine burial sites outside Iguala where drug cartels are believed to dump their enemies.

One forensic expert, who works with federal investigators, said identification is an arduous process that takes time. Charred remains like those recovered at the first mass graves can leave very little DNA for testing.

"If a bone is burned at more than 300 degrees, it's almost impossible to identify because the collagen is burned. Because of that, criminal organizations started to adopt that technique," said Jorge Arturo Talavera, head of the bio-archaeology team at the Mexico's National Institute of Anthropology and History.

He said the way the remains are exhumed also can affect identification. If they're pulled out in a hurried manner, other identifying articles like jewelry or teeth get discarded.

Hundreds of teachers, students and relatives of the missing marched to the center of the state capital, Chilpancingo, on Tuesday, taking a much more solemn tone after angry protests and vandalism Monday that badly damaged the state capital building and other government buildings.

They lined up in silence as organizers passed out white flowers. Some carried candles with a sprawling billboard offering a 1 million peso ($75,000) reward for information.

Rodriguez, 46, said he felt empowered by the march. He and his wife and daughter have been coming to the school every morning for any news. Rodriguez has a truck and sells jugs of water. His wife makes and sells tortillas.

Standing beside the college's basketball court, where families lined up for a simple meal of chicken, rice and tortillas, Rodriguez explained that his son started his first year at the school in July. He wanted to study to help his family get ahead, especially his three sisters, Rodriguez said.

"We're a humble family," Rodriguez said.

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Associated Press writer E. Eduardo Castillo reported this story in Mexico City and Christopher Sherman reported in Tixtla.