Mexico's attorney general, Jesus Murillo Karam, has confirmed that a bone fragment found near a garbage dump belongs to one of 43 students who disappeared in September from the city of Iguala.
Murillo identified the body part as belonging to Alexander Mora. Austrian forensic experts working with Mexican authorities made the identification.
The attorney general says the bone fragment was found among ashes and charred remains near a river and garbage dump where members of a drug gang allegedly killed the students and burned their bodies.
Authorities believe Iguala's mayor, Jose Luis Abarca, and his wife ordered police to round up the leftist students and turn them over to the drug gang.
So far, 80 people have been arrested, including the mayor and his wife and a number of police and gang members.
The grisly case has infuriated Mexicans who say they are sick of corruption by local officials. It also has shaken President Enrique Pena Nieto, whose government is accused of waiting too long to begin a federal investigation.
Some of the parents of the missing students are demanding that the president resign.