Mexican President Enrique Pena Nieto wants answers.
Dozens of students -- 43 in all -- have gone missing and now authorities in the restive state of Guerrero have found mass graves with the charred remains of up to 28 people.
Officials think the bodies of the missing students were likely among those charred corpses.
They suspect local security officials of conspiring with gang members to kill them.
Pena Nieto says he wants the perpetrators brought to justice.
(SOUNDBITE) (Spanish) MEXICAN PRESIDENT ENRIQUE PENA NIETO, SAYING:
"We must find out the truth and ensure that the law is enforced against those responsible for these acts which are truly outrageous, painful and unacceptable."
Authorities say some 30 suspects have been arrested in connection with the disappearances, including the head of security for the municipality where the students went missing as well as 22 police officers.
But in the town of Tixtla, where many of the students
