Two Mexican gang hitman admitted to receiving help from security officials in the slaughtering 17 of the 43 students who went missing after a Sept. 26 clash with police in the state of Guerrero, the state's attorney general Inaky Blanco said on Sunday.
Mexican President Enrique Peña Nieto followed on Monday with a statement vowing to find those responsible.
"Mexican society and the families of the youths who are regrettably missing rightly demand that the incidents be cleared up and that justice be served," he said during his televised speech. "We need to find the truth and make sure the law is applied to those responsible for these outrageous, painful and unacceptable acts."
A mass grave containing charred human remains was found over the weekend near the town of Iguala.
Twenty-eight bodies have been found at the site so far, according to Blanco, who said that it's "probable" that some of the missing students are among the remains. DNA test results will take at least two weeks, according to authorities. Blanco said the motives of the killings is not yet clear.
The governor of Guerrero state, Angel Aguirre, said he believes the students were killed by gangs operating in tandem with the police, and two of the gang's hitmen reportedly admitted to investigators that they were ordered to the site of the shootings by Iguala's public security director.
Blanco also stated he believes the leader of the local Guerreros Unidos gang conspired with security officials to commit the killings, reported Reuters. Clashes that night left six dead, 25 wounded and 43 missing.
Thirty people have been detained in connection with the shootings, and at least 22 police officers have been arrested, according to Reuters. The mayor of Iguala, Jose Luis Abarca, and the public security chief are also being investigated for their possible involvement.