The parents' comments yesterday came a day after a group of international experts issued a report criticising the investigation, saying suspects appear to have been tortured and key pieces of evidence related to the supposed burning of the students' bodies were not correctly investigated.
The 43 students at the radical teachers' college of Ayotzinapa have not been heard from since they were taken by local police in late 2014 in the city of Iguala in southern Guerrero state. The government says corrupt police turned them over to a drug gang, which killed them and burned their remains in a dump in the town of Cocula. Parents reject that conclusion and experts say there is no proof of it.
The group of experts said the bags of bone fragments were found at a different spot and time than authorities had said, and that outside experts weren't immediately allowed access to the site.
"They were the ones who planted the evidence in the San Juan river," said Gonzalez, the father of missing student Cesar Manuel Gonzalez.
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The Inter-American Commission on Human Rights expert group says that a study of 17 of the approximately 123 suspects arrested in the case showed signs of beatings, including, in some cases, dozens of bruises, cuts and scrapes.
Human rights activist Mario Patron of the Miguel Agustin Pro Juarez center said the torture allegations "endanger efforts to find the truth."
The Mexican government recently released documents suggesting investigations had been opened against police and military personnel, but authorities have not answered requests about whether anyone has been arrested or charged.
Betanzos called the case "the most exhaustive investigation in the history of Mexican law enforcement.