After testing remains found in nine mass graves in southern Mexico, authorities announced Tuesday that they have yet to find any of the 43 missing college students who disappeared after a clash with police nearly three weeks ago.
Forensic investigators tested 28 charred bodies found in graves that were unearthed last week, and announced the discovery of a 10th grave as well, reported the Associated Press.
Attorney General Jesus Murillo Karam said an additional 14 police officers were arrested and confessed their involvement in the disappearance, bringing the total number of detainees held under suspicion of involvement to 50.
The mayor and police chief of Iguala are currently on the run from authorities, and are accused of being linked to local drug gang, Guerrero Unidos, who are suspected to have colluded with police in the kidnappings.
Karam said no motives or masterminds have been identified, but he believes police-gang collusion is a given.
"There's a connection. We will determine if it was coordination or subordination, but it's clear to me that they were working together," Karam said of police and drug traffickers.
Many of the bodies at the first grave site appear to have been buried months ago, said Guerrero Gov. Angel Aguirre, suggesting that they were likely earlier victims of the gangs.
Recovering DNA from charred remains is a slow process, sometimes leaving little to no DNA for testing, one forensic expert working with federal investigators told the Associated Press.
"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," Jorge Arturo Talavera, head of the bio-archaeology team at the Mexico's National Institute of Anthropology and History, told the Associated Press.
After around 100 students hijacked buses to return to their campus, police opened fire, killing six people, wounding 25 and arresting dozens.
