An independent commission has rejected the Mexican government’s investigation into 43 college students who vanished in southwestern Mexico last year. The report issued by experts assembled by the Inter-American Human Rights Commission calls into question several of the government’s assertions about the students’ disappearance, the Associated Press reported.

The Mexican government claims police in Iguala, Guerrero, mistook the students as rivals of a local militia, Guerreros Unidos, and then handed them over to the gang. But their abduction more likely has to do with the buses the group commandeered Sept. 26 as transport to a local demonstration. The student group may accidentally have interfered with a drug shipment in one of the buses, the report said. Guerreros Unidos is thought to be one of many groups behind the trafficking of heroin into the United States, the Chicago-Sun Times reported. Additionally, the report debunks the claim the students were incinerated in a garbage dump in the nearby town of Cocula.

"There is no evidence that supports the hypothesis, based on testimonies, that 43 bodies were cremated in the municipal dump of Cocula on Sept. 27, 2014," authors of the report said, according to Reuters.

In response to the report, the Human Rights Commission blasted the Mexican government for its handling of the investigation.

"This report provides an utterly damning indictment of Mexico's handling of the worst human rights atrocity in recent memory," Jose Miguel Vivanco, Americas director at Human Rights Watch, said in a statement to the Associated Press. "Even with the world watching and with substantial resources at hand, the authorities proved unable or unwilling to conduct a serious investigation."

Despite nearly a year passing since the students’ disappearance, what happened to them still is unknown, the 400-page report said. Lawyers representing the families of the students who disappeared took aim at the Mexican government Saturday for losing evidence and failing to provide scientific proof to back up its account of how the students were abducted and then incinerated.