Mexican President Enrique Peña Nieto vowed on Monday to hunt down those responsible for the apparent massacre of dozens of students in the southwest of the country that authorities say involved local security officials.
The students went missing after they clashed with police in Iguala in the volatile, gang-ridden state of Guerrero on Sept. 26. A mass grave was found near the town over the weekend, full of charred human remains.
Guerrero's attorney general, Inaky Blanco, said on Sunday that 28 bodies have been found at the site so far, and it is "probable" that some of the missing 43 students are among the remains found in the graves.
He said the motive of the killings was unclear.
Other local officials, speaking on condition of anonymity, told Reuters that at least 34 bodies have been discovered.
In his first comments on the incident, Peña Nieto said the federal government would identify those behind the massacre and make sure they face justice.
"We need to find the truth and make sure the law is applied to those responsible for these outrageous, painful and unacceptable acts," he said in a four-minute-long televised statement. He did not take questions.
Blanco said on Sunday that two gang hitmen have admitted killing 17 of the missing students with the help of security officials.
The likelihood of official involvement creates a major headache for Peña Nieto, who has sought to shift attention away from Mexico's gangland violence and onto a batch of economic reforms he has driven through Congress.
Angel Aguirre, the governor of Guerrero state, said he was certain the students were killed by gangs in cahoots with the police. He added that he expected at least some of the bodies in themass grave would be those of the students, but said tests still needed to be completed to make sure.
"It could well be them, I don't rule it out, it's a very real possibility," Aguirre, who has been criticized for not doing enough to clean up the state and keep a lid on the rampant violence, said in a radio interview.
Some 22 local police have been arrested in connection with the violent incidents in Guerrero.
The fugitive mayor of Iguala, Jose Luis Abarca, is also being investigated for possible involvement in the crimes, as is the head of security for Iguala.
Blanco said the leader of a local gang known as the Guerreros Unidos conspired with security officials to carry out the killings.
Peña Nieto took office two years ago pledging to end a wave of violence that has killed around 100,000 people since the start of 2007. Though homicides have fallen on his watch, other crimes have increased, including extortion and kidnapping.
Guerrero, which is also home to the resort of Acapulco, has been one of the most lawless states in Mexico for years.
The federal takeover of the area came amid rising international concern over two possible cases of mass killings involving Mexican authorities. In addition to the Iguala incident, an army unit is now under investigation and three soldiers face homicide charges in a June 30 confrontation that killed 22 suspected gang members in neighboring Mexico state.
The army originally reported that the 22 died in a gun battle after soldiers on patrol came under fire. But a witness told The Associated Press that 21 of them were killed after they surrendered.
On Monday, Iguala's remaining police force was sent to a training center, and officers' weapons will be checked for evidence of being used in crimes, said National Security Commission Monte Alejandro Rubido.
Guerrero Gov. Angel Aguirre charged last week that the majority of police in his state have been coopted or infiltrated by organized crime.
This report contains additional material from The Associated Press.