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As Colombia grieves over the death of 32 children after the youngsters crammed into a bus that eventually caught on fire, authorities filed charges against the vehicle's driver.

The children, who range in age from toddlers to 12, were on their way home from Sunday school classes at a small Pentecostal church when the driver decided to exit the vehicle and put in gas in its tank from a portable container.

Colombian authorities said Monday night that aggravated manslaughter charges would be filed against a bus driver. Luz Estella Duran, mayor of the village of Fundacion where Sunday's tragedy took place, said witness accounts suggested the driver might have left the small bus running with the children on board when he made the fatal decision to put gas in the bus.

Twenty others were hospitalized, with about half in a delicate state, Duran said.

President Juan Manuel Santos interrupted a busy final stretch of campaigning ahead of the May 25 elections and traveled Sunday night to the town near the Caribbean coast to pay his respects to the mostly poor families of the victims. He called for a thorough investigation to prevent more such tragedies and declared a national day of mourning.

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"We are with you. The entire country is with you," Santos said.

The students had been at a church down the road from a nearby town where Nobel Prize-winning author Gabriel Garcia Marquez was born.

Nelson Tapias, a 54-year-old merchant in the town, said he lost his granddaughter and several nephews. "I have my heart torn apart in six pieces," he told The Associated Press in a phone interview.

Bus accidents are frequent in Colombia, especially in poorer, rural areas like the one near Fundacion where safety inspections and transit laws are rarely enforced.

Gen. Carlos Mena, the highway police commander overseeing operations in Fundacion, said the driver was operating the bus without a license or mandatory insurance. The 1993 Dodge's registration papers were also out of date and the bus was carrying twice the maximum number of passengers allowed.

Authorities would not say where the driver, identified as Jaime Gutierrez, was being held, for fear he could be harmed by outraged residents in the rural town of 80,000 people.

The whereabouts of the pastor, Roberto Padilla, was also unknown.

"Last night they wanted to burn him alive, so for his own safety they removed him from the town," said Fanny Valseiro, who has been attending services at the church for more than a decade.

Padilla, in a radio interview from an undisclosed location, said that the he and the rest of the church leadership were unaware of the bus driver's violations.

Prosecutors said late Monday that they also planned to press charges against Manuel Ibarra, a member of the congregation who was responsible for contracting the bus.

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