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Eduardo Verdugo, Associated Press
Demonstrators holding posters of Mexico's President Enrique Pena Nieto, right, and Attorney General, Jesus Murillo Karam, left, march in protest for the disappearance of 43 students in the state of Guerrero, in Mexico City, Wednesday, Nov. 5, 2014. The posters read in Spanish "It was the state." Federal police detained yesterday Iguala Mayor Jose Luis Abarca and his wife, Maria de los Angeles Pineda, who are accused of ordering the Sept. 26 attacks on teachers' college students that left six dead and 43 still missing.

MEXICO CITY — Suspects in the disappearance of 43 college students have confessed to loading the youths onto dump trucks, murdering them at a landfill, then burning the bodies and dumping the ashen remains into a river, Mexican authorities said Friday.

In a somber, lengthy explanation of the investigation, Attorney General Jesus Murillo Karam played video showing hundreds of charred fragments of bone and teeth fished from the river and its banks. He said it will be very difficult to extract DNA to confirm that they are the students missing since Sept. 26 after an attack by police in the southern state of Guerrero.

"I know the enormous pain the information we've obtained causes the family members, a pain we all share," Murillo Karam said at a news conference. "The statements and information that we have gotten unfortunately point to the murder of a large number of people in the municipality of Cocula."

Some 74 people have been detained so far in a case. Authorities say it said started when police, under orders of the former Mayor Jose Luis Abarca and working with a drug gang, opened fire on students in the city of Iguala, where they were collecting donations and had commandeered public buses. Six people were killed in two confrontations before the 43 were taken away and handed over to members of the Guerreros Unidos cartel. Abarca and his wife are among those arrested.

Murillo Karam said authorities are searching for more suspects.

The parents, human rights groups and Mexicans in general have been appalled by the government's slow response to a case that has exposed in the worst way decades of collusion between officials and organized crime along with government inaction. There had been accusations for more than a year that Abarca was involved in killing and disappearing rivals but no investigation. When students who survived the Iguala confrontation sought help from the military the night of the attack, they said they were turned away.

Parents reacting to Murillo Karam's report Friday said they have lost trust in anything the government says.

"As long as there are no results, our sons are alive," Felipe de la Cruz, the father of one of the disappeared. "Today they're trying to close the case this way ... a blatant way to further our torture by the federal government."

In the most comprehensive accounting to date of the disappearances and the subsequent investigation, Murillo Karam showed videotaped confessions by those who testified they used dump trucks to carry the students to a landfill site in Cocula, a city near Iguala. About 15 of the students were already dead when they arrived at the site and the rest were shot there, according to the suspects.

They then built an enormous funeral pyre that burned from midnight until 2 or 3 p.m. along the River San Juan in Cocula. "They assigned guards in shifts to make sure the fire lasted for hours, throwing diesel, gasoline, tires, wood and plastic," Murillo Karam said.

The suspects even burned their own clothes to destroy evidence, they said.

It was about 5:30 p.m. when the ashes had cooled enough to be handled. Those who disposed of the bodies were told to break up the burned bones, place them in black plastic garbage bags and empty them into the river.

Murillo Karam said the teeth were so badly charred that they practically dissolved into dust at the touch.

"The high level of degradation caused by the fire in the remains we found make it very difficult to extract the DNA that will allow an identification," he said.

Murillo Karma had told relatives of the missing students earlier Friday that authorities believe their children are these charred remains, but have no DNA confirmation.

Murillo Karam also confirmed at the news conference that human remains found in mass graves discovered after the students went missing did not include any of the 43 young men enrolled at a radical rural teachers college. Those graves held women and men believed to have been killed in August, he said.

Among the bodies found in the course of the investigation were a father and son. By searching for reports of father-son disappearances, authorities were able to make a positive identification. Murillo Karam said the victims, whose names he did not use, apparently made a call before disappearing to say they were being detained by Iguala police.

Associated Press writer Christopher Sherman contributed to this report.