MEXICO CITY — An international committee of experts reviewing the case of 43 missing college students whose disappearance last fall traumatized Mexico said Sunday that there was no evidence to support the government’s conclusion that the students were executed by a drug gang that then burned the bodies to ashes in a garbage dump.

Not only did physical evidence contradict the government’s version of what happened to the students, but the review showed that federal police and soldiers knew that the students were being attacked by the municipal police and failed to intervene.

The report’s conclusions were a sharp rebuke to the government of President Enrique Peña Nieto, which had sought to put the case to rest. Its release could rekindle the widespread anger and incredulity that flared in the weeks after the students vanished from Iguala in the southern state of Guerrero last Sept. 26.

That episode helped shatter the image that the president had worked hard to establish — as a modern young reformer poised to turbocharge Mexico’s economy, and it thrust the nation’s chronic afflictions of organized crime and corruption back into the public consciousness.