Fifteen charred bodies found in a burned-out bus in eastern Guatemala were shot before being set on fire, prosecutors said Monday.

Police spokesman Donald Gonzalez said the killings may have been drug related. He said parts of the vehicle, which originated in Nicaragua, had been violently torn away, as if someone was looking for secret compartments.

At least 14 of the dead were Nicaraguan, including the driver, said Attorney General Amilcar Velazquez.

A Dutchman was on board when the bus arrived in Guatemala, according to a passenger list released by the government. None of the bodies has been positively identified, however.

The bus left Nicaragua with 16 passengers, but only 15 bodies were found after the vehicle burned on Saturday on an unpaved road in a mountain valley about 90 miles (140 kilometers) east of the capital, Guatemala City.

It is unclear what happened to the other passenger. Authorities received more human remains Monday and were examining them to determine if they belonged to a 16th person, said National Forensic Institute spokesman Fernando Lucero.

Velazquez said bullets and shell casings were found at the scene, and authorities have confirmed the victims were shot, explaining why there were no signs that anyone tried to flee the burning vehicle. All the dead were found in their seats.

The bus was on a charter route that carried Nicaraguan vendors to Guatemala, where they would buy things to sell at home.

Driver Carlos Paiz had driven the same route every weekend for the past four years, according to a relative, Donald Sandoval, who said he didn't know why the bus was targeted.

"It was a bus that left from (Nicaragua) and anyone could get on," he said.

Guatemala has struggled with growing drug and gang violence.

In March, near where the bus was found, 11 people were killed in a gang fight in which several vehicles were set on fire.

And the charred bodies of three Salvadoran members of the Central American Parliament were found along a rural road in February 2007.