Evidence and testimony "fully" confirm that all 43 of the students abducted Sept. 26 in the southern state of Guerrero were killed, Mexican Attorney General Jesus Murillo Karam said Tuesday.
Thanks to an extensive investigation, it "has been proven" that the 43 students from Ayotzinapa teachers college were seized by municipal police in Iguala, Guerrero, and handed over to members of the Guerreros Unidos drug cartel, who murdered the youths, burned the bodies at a dump in the nearby town of Cocula and dumped the bones into the San Juan River, the attorney general said.
Forensic tests show the bodies were incinerated in a pit 40 meters (131 feet) deep, he told a press conference.
The blaze, fueled by tires and kindling, reached a temperature of 1,600 C (2,911 F) and raged for more than 12 hours, Murillo Karam said.
The heat of the fire rendered most of the remains recovered from the river unsuitable for DNA testing and the 17 fragments sent to a specialized laboratory in Austria for analysis were "those that had the greatest possibility of being identified," he said.
The Austrian lab was able to match the remains to only one of the missing students, Alexander Mora.
Tests of the other remains using a new procedure are in progress, but the results will be slow in coming, the attorney general said.
The Ayotzinapa students were slain because Guerreros Unidos leaders believed that members of the rival Los Rojos cartel had infiltrated the teachers college, according to the government's account.
Murillo Karam, however, said Tuesday that authorities have not been able to connect any of the students to "any criminal group."
While 99 people are in custody in connection with the massacre, including ousted Iguala Mayor Jose Luis Abarca and wife Maria de los Angeles Pineda, six other suspects remain at large.
The federal government says the couple had ties to Guerreros Unidos and that the mayor ordered the students killed to prevent them from disrupting a political speech to be given by Pineda on the night of Sept. 26.
Families of the students remain unwilling to accept that version of events and are demanding to know why soldiers of the Iguala-based 27th Infantry Battalion who witnessed the police attack did not intervene.
Respected newsweekly Proceso published last month a story drawing on a confidential Guerrero state government document that points to Mexico's Federal Police as the perpetrators of the slaughter of the 43 students.
Early in December, a group of scientists at the National Autonomous University of Mexico said that Murillo Karam's account of the burning of the students' bodies "has no support in facts or in physical, chemical or natural phenomena."
Jorge Antonio Montemayor, a research physicist said the evidence provided by the AG's office indicated the bodies were incinerated in a modern crematorium, not a rural dump.