Mexican authorities have found bodies that were shot, burned in a garbage dump and thrown in a muddy river in black plastic bags — presumably the remains of at least some of the 43 students who disappeared in September — the attorney general said in a news conference Friday.

Without providing conclusive evidence about the identities of the bodies, Attorney General Jesús Murillo Karam laid out the most detailed account yet of the likely fate of the teachers’ college students who went missing in the state of Guerrero. Using video clips of detainees’ confessions, including their re-creations of how they carried out the killings, Murillo Karam presented a grim account of the brutal violence that took place over two days and involved police and drug gang members. Murillo Karam, in his roughly hour-long presentation, said that many of the remains were burned to such a degree that identifying DNA has been difficult.

“The testimony very unfortunately points to the homicide of a large number of people,” Murillo Karam said.

The disappearance of so many young students — and the involvement of corrupt government officials — has horrified Mexico and created a weeks-long political crisis. Tens of thousands of protesters have marched in the capital and around the country demanding answers and justice. Protesters have burned government buildings in Guerrero and students at universities across the country have gone on strike. The fallout from the case, Murillo Karam said, would change many things about Mexico.

“It’s sad to show these images, but it’s our duty to society, which is truly offended,” he said. “This cannot be repeated.”

Some relatives of the missing students rejected the government’s findings and said they have demanded more explicit scientific evidence before they would accept that the students were dead.

“Since there is no proof, our children are alive,” Felipe de la Cruz, a spokesman for the relatives, told reporters.

In late September, Iguala Mayor Jose Luis Abarca ordered that the students, traveling in four vehicles, be stopped from coming into town and disrupting a speech by his wife, Maria de los Angeles Pineda, authorities said. In the ensuing confrontation with police, six people were killed and 43 others were hauled away and turned over to the drug gang Guerreros Unidos.

In his presentation, Murillo Karam said that young people were taken in police trucks to an area between Iguala and Cocula, where they were handed over to Guerreros Unidos cartel members. From there, they were taken to a garbage dump in Cocula. By that point, about 15 of them were already dead or unconscious, including by asphyxiation, Murillo Karam said. The survivors were forced onto their knees and shot. In the trash dump, the killers stacked the bodies into a pile of wood, plastic and tires, doused them in diesel and gasoline, and set them ablaze.

When the fire subsided hours later, the detainees explained they then packed the remains, including ash and teeth, into black plastic bags, breaking bones when necessary to fit them into the sacks. These sacks were then thrown into the nearby Rio San Juan, where investigators retrieved some of them.

Since the students’ disappearance in September, the search across Guerrero has involved as many as 10,000 Mexican police officers, soldiers and other investigators. In the process, they found mass graves from older killings, but for weeks failed to find any trace of the students.

Earlier this week, Abarca and his wife were captured in a police raid of a Mexico City safe house, two of the 74 arrests so far in the case. About a week ago, authorities had also detained three apparent witnesses, who recounted in detail their participation in the crime.

They were identified Friday as Patricio Reyes Landa, “El Pato”; Jonathan Osorio Gomez, “El Jona”; and Agustin Garcia Reyes, “El Sheriff.”

“They are members of Guerreros Unidos, and they confessed that they had received and executed a group of people that were given to them by municipal police of Cocula,” Murillo Karam said.

Murillo Karam said the investigation will continue and there are arrest warrants for another 10 people.

The remains will be sent to a laboratory in Austria to work on the identifications.