19 weeks ago, 43 Mexican students disappeared. What happened?

WATCH ABOVE: Parents of missing 43 Mexican students want case to remain open

TORONTO – It’s been more than four months since 43 college students went missing in the southern Mexican state of Guerrero. The country’s attorney general says they’re dead. Some are calling for a further investigation.

On Tuesday, Mexico’s Attorney General Jesus Murillo Karam publicly stated for the first time that all 43 students have died since being abducted Sept. 26, 2014 in the city of Iguala.

That night, Murillo Karam said, police handed the students over to a local gang, known as Guerreros Unidos, who killed them, burned the bodies at a dump and tossed the remains into a river.

WATCH: Mexico’s human rights committee president urges authorities not to close case on missing students

But despite DNA tests, officials have only been able to positively identify one of the students from the charred remains that have since been recovered. Their families, human rights activists and the Canadian government say more evidence is needed before declaring all 43 deceased.

So far 99 people have been detained in connection with the students’ disappearance, including the former mayor of the city of Iguala, Jose Luis Abarca.

During an emotional press conference Tuesday evening, parents accused the government of trying to quickly wrap up the investigation.

“We don’t believe anything of what they say,” said Carmen Cruz, mother of 19-year-old Jorge Cruz, one of the disappeared students. “We are not going to allow this case to be closed.”

Human Rights Watch issued a statement Wednesday questioning the attorney general’s investigation, which the group says relied on confessions extracted through pressure or torture from gang suspects.

IN PHOTOS: Mexican protesters take part in a march commemorating the 43 students who disappeared

At a press conference Wednesday, the president of Mexico’s National Commission of Human Rights said authorities have much more explaining to do.

“It should be noted that once the investigations are carried out, the authorities may not close this case until all those responsible are prosecuted and the fate of the missing students is clarified.” Luis Raul Gonzalez Perez told reporters.

“What happened in Iguala is the most significant example of what is wrong in our society, especially the infiltration of organized crime in some state structures.”

The case has sparked vocal, often violent protests across Mexico with many questioning the official story and the possible involvement of federal authorities. It has also engulfed the presidency of Enrique Peña Nieto.

WATCH: Violent protests urging president to resign continue in Mexico

Alex Neve, secretary-general of Amnesty International Canada, says the Canadian government needs to take a more active role in the devolving human rights crisis in Mexico.

“We’re concerned about the lack of action taken by the Canadian government. We’ve highlighted that Canada has an important role to play in taking action in Mexico,” Neve told Global News.

“For many years Canada has not pushed as much as the crisis as it requires. Sadly it’s reflective of a scenario not unique to Canada and not unique to Mexico. Human rights issues often slip into the backseat, if not in the trunk.”

Neve says that as a North American Free Trade Agreement partner Canada could be a force for change in the country.

“The close and increasingly interconnected relationship with Mexico carries with it a chance to push for change on the issue of human rights,” he said. “From both of its NAFTA trading partners, Mexico could be hearing something. But it’s hearing nothing.”

U.S. President Barack Obama and Peña Nieto briefly discussed the missing students in early January. Obama called it “a tragedy” and offered his support.

While no official motive as to why the students were attacked, Murillo Karam said he believed the Guerreros Unidos mistook the students for a rival gang. Others believe they were targeted for a different reason.

Sergio Rivera-Ayala, a professor of Latin American studies at the University of Waterloo, says one the reasons the students who were attending the Raúl Isidro Burgos Rural Teachers’ College of Ayotzinapa were targeted was their opposition to government policies.

IN PHOTOS: Protests in Mexico have been ongoing since the fall of 2014

Judith Teichman, political science and international development professor at the University of Toronto, said the deteriorating situation in Mexico should concern Prime Minister Stephen Harper.

“Things are going to hell in a handbasket,” Teichman said. “The drug cartels are spread throughout Mexico. Things are really bad in the northern states near the U.S. border and there’s increasing guerrilla activity in the southern states.”

Teichman said preoccupation with other international conflicts – in the Middle East, for example – has meant Canada and the U.S. have paid scant attention to security concerns much closer to their own borders.

A spokesperson for Canada’s Department of Foreign Affairs said the federal government is “deeply concerned” about the violent events in Iguala.

“Our hearts go out to the families of the students,” said John Babcock, in an email statement. “Canada is encouraged by Mexico’s stepped-up plans to bolster rule of law in Mexico through significant security and justice reforms and we welcome their efforts to bring greater transparency to the investigation process and commitment to holding the perpetrators to account.‎”

On Jan. 31 Foreign Affairs Minister John Baird will travel to Boston where he will meet with Mexico’s Secretary of Foreign Affairs José Antonio Meade and U.S. Secretary of State John Kerry to discuss “global and regional issues, including security challenges and the competitiveness of North America.”

*With files from the Associated Press