David Agren

Special for USA TODAY

MEXICO CITY — The 43 students missing for more than six weeks are believed dead after charred human remains were fished from a river and its banks, Mexico's attorney general said Friday.

Extracting DNA will be incredibly difficult after the bodies and other evidence was burned for the better part of a day prior to being tossed in the water, Attorney General Jesús Murillo Karam said at a press conference, adding many of the victims' teeth had "turned to powder."

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

The announcement came after confessions by members of the Guerreros Unidos cartel accused of burning the victims' bodies using gasoline, kindling and tires to keep the fire going, Murillo Karam said. Municipal police handed over the students — some dead, some unconscious — to the gang after a Sept. 26 attack in Iguala, in the southern state of Guerrero, he said.

Authorities have arrested 74 suspects, including Iguala Mayor José Luis Abarca and his wife, María de los Ángeles Pineda. The couple are accused of ordering the assault on the students — whom the pair claimed were coming to interrupt a public party thrown by Pineda. At least 10 more suspects remain at large, Murillo Karam said.

During the press conference, Murillo Karam played video showing charred fragments of bone being pull from the River San Juan in Cocula, located near Iguala. Confessions of suspects testifying to loading the students in dump trucks before taking them to a landfill site there were also shown.

According to the tapes, 15 students were already dead when they arrived at the site, and the rest were shot, the suspects said. A large funeral pyre was then built and burned from midnight until 2 p.m. or 3 p.m along the river.

After the ashes had cooled around 5:30 p.m., the suspects who disposed of the bodies were told to break up the burned bones, place them in garbage bags and dump them in the river.

Classmates say the students went to Iguala on borrowed buses to collect funds for a future trip to Mexico City, but were stopped by police and shot in an incident that left six dead, including three students.

The case has caused soul searching in Mexico, where an estimated 100,000 people have lost their lives over the past eight years in crimes committed by drug cartels and organized criminal groups. Another 30,000 people have disappeared.

"I'm truly outraged and sad. I suppose that Mexican society is the same," Murillo Karam said during the hour-long press conference in Mexico City.

President Enrique Peña Nieto, who had previously remained silent on security matters since assuming office in December 2012, spoke after the attorney general, pledging to punish those responsible for the vicious crime.

Students across the country have marched in the streets and closed their schools, demanding information about the missing.

"This country keeps getting increasingly worse," said chemistry student Maite Gonzalez, 21, who marched Thursday with thousands of other young people through central Mexico City. "This happens often. Not just in Guerrero."

Parents of the missing students expressed anger with federal officials, saying authorities didn't act quickly and weren't keeping them properly informed.

The students hailed from farm families and attended a college that trained teachers to give classes in impoverished pockets of Guerrero state, which is located to the south of Mexico City and includes some of the countries most marginalized municipalities.

Even as the attorney general announced his findings Friday, families of the missing expressed skepticism of the government's version of events, saying they want to see scientific proof instead of confessions.

"We believe that they're alive, and we want them brought back alive," said Felipe de la Cruz, one of the parents of the missing students. "We believe in God that they're alive."

Contributing: The Associated Press