Human rights groups criticized Mexico's government on Wednesday for concluding that 43 students missing since September were killed, saying it was premature because unanswered questions remain in the case.
Human Rights Watch and Amnesty International issued separate statements questioning the conclusions of Attorney General Jesus Murillo Karam in a case that has engulfed President Enrique Pena Nieto in the biggest crisis of his administration.
Both international organizations said the investigation relied mostly on confessions from gang suspects, who said they killed and incinerated the students after they received them from corrupt local police in southern Guerrero state.
Jose Miguel Vivanco, Americas director at New York-based HRW, said the investigation generates "a lot of skepticism and many doubts."
"We know that in Mexico confessions are extracted on the basis of pressure, torture and irregularities," Vivanco told MVS radio.
Amnesty International said Murillo Karam's conclusion was "premature and risks curtailing a full and thorough investigation into this tragedy."
"If the attorney general hopes that this announcement will draw a line under this tragedy then he is wrong. There are still many, many questions left unanswered, including the possible complicity, by action or omission, of the army and other authorities in the attack against these young student teachers," said Erika Guevara-Rosas, Americas Director at London-based Amnesty.
Murillo Karam said on Tuesday that there was no evidence of any role by the army, which has a base in the city of Iguala, where the 43 young men were attacked on September 26.
Karam concluded that he now had "legal certainty" that all 43 aspiring teachers were kidnapped by municipal police, handed over to the Guerreros Unidos drug gang, slaughtered and set ablaze in a bonfire of tires and fuel.
An Austrian laboratory was only able to identify one of the students and said the other remains sent by the Mexican authorities were in such bad shape that they lacked useable DNA.
Families of the students refuse to believe their sons are dead until they shown scientific proof.