For 50 days, Epifanio Alvarez has had trouble eating and sleeping, tortured by uncertainty over what happened to his son Jorge and 42 other students missing in Mexico.
Alvarez refuses to believe the young men were slaughtered by drug gang henchmen, and is clinging to the hope that this explanation is a cover-up by a government he and the other parents deeply distrust.
"The nights are hell. We sleep one or two hours and wake up. We can't rest. It's always on our minds: Where is our son?" said Alvarez, a strapping 46-year-old.
Like the other parents of the 43 students who went missing in the southern state of Guerrero on September 26, Alvarez's agony has been compounded by the feeling that the truth is being hidden.
He says officials' version of events -- that hitmen from the Guerreros Unidos drug gang confessed to killing the students and incinerating their bodies -- is undermined by previous versions that turned out to be false.
Initially, policemen arrested for opening fire on the students' bus and handing them over to the drug gang told investigators the missing men had been killed and buried in mass graves around the town of Iguala.
But forensic testing on 24 bodies found in these graves showed they were not those of the students.
"They already tricked us last time. They need to give us back our sons and stop playing with our emotions," Alvarez told AFP.
Attorney General Jesus Murillo Karam told the parents last week that the alleged Guerreros Unidos hitmen had confessed to receiving the students from police, taking them to a landfill, killing them, burning their bodies in a funeral pyre and tossing bags of remains into a river.
But that story does not hold water, Alvarez said.
"We don't believe it. It was raining the night they say they killed them. How could they have made such a big fire? How could they have made the bones disappear? The only way would be to grind them up," he said.
- 'Powerful interests at play' -
Authorities say the missing men -- students at a teacher-training college known for its radical politics -- vanished after police shot at their buses in Iguala, killing six people, and delivered the remaining 43 to the Guerreros Unidos.
Prosecutors say the city's mayor ordered police to confront the students over fears they would disrupt a speech by his wife.
The government has stopped short of declaring them dead, saying it will wait for DNA results of remains that have been sent to forensic specialists at the University of Innsbruck in Austria.
But it has downplayed the chance of identifying the charred remains found in plastic bags along the San Juan River, saying only two bones were salvageable for testing.
That has fed parents' fears that President Enrique Pena Nieto's government is simply trying to close the case, which has sparked violent protests across the country.
"We want evidence. To us, they've been kidnapped. They abducted them and handed them over. They're in cahoots with the mafia," said Berta Nieves, whose son was one of those killed in the initial shooting.
The parents have a range of theories on their sons' whereabouts. Some think corrupt police are holding them. Others think it is the government.
"We're almost certain they're out there somewhere. There are very powerful economic and political interests at play. The bit about the bonfire is just government theatre to make us give up," said Felipe de la Cruz, spokesman for the parents.
Some parents have returned to the site where the students were allegedly burned, seeking evidence that might give them some form of closure.
Others have accompanied federal police on helicopter, boat and horseback patrols, criss-crossing the Guerrero countryside looking for any sign of their sons
But they have little faith in the government.
On Thursday, the parents launched a protest tour, forming three bus convoys that plan to converge on the capital next week, spreading the message across Mexico that their sons are still missing.