People demonstrate to demand for justice in the case of the 43 missing students from Ayotzinapa teachers' training college, in Mexico City January 26, 2015. [Photo/Agencies]

MEXICO CITY - Investigators are now certain that 43 college students missing since September were killed and incinerated after they were seized by police in southern Guerrero state, the Mexican attorney general said Tuesday.

It was the first time Jesus Murillo Karam said definitely that all were dead, even though Mexican authorities have DNA identification for only one student and a declaration from a laboratory in Innsbruck, Austria, that it appears impossible to identify the others.

The attorney general cited confessions and forensic evidence from an area near a garbage dump where the Sept 26 crime occurred that showed the fuel and temperature of the fire were sufficient to turn 43 bodies into ashes.

"The evidence allows us to determine that the students were kidnapped, killed, burned and thrown into the river," Murillo Karam said in a press conference that included a video reconstruction of the mass slaying and of the investigation into the case.

He added that "there is not a single shred of evidence that the army intervened ... not a single shred of evidence of the participation of the army," as relatives of the victims have claimed.