Thousands of protesters marched to the federal elections office in Mexico City on Thursday to mark the six-month anniversary of the disappearance of 43 missing college students in northern Guerrero, a notorious gang- and drug-ridden southwestern state in Mexico.

The 43 student-teachers disappeared after allegedly being kidnapped by local police and handed over to gang members to be brutally murdered on Sept. 26, 2014.

Police initially opened fire and killed six students before rounding up the survivors and handing them to a local drug-trafficking gang known as Guerreros Unidos. The gang then burned the victims on a pyre and pulverized their teeth and bones to prevent them from being identified.

Following the egregious act of violence, which sparked international outrage and protest, authorities charged the former mayor of the southern Mexican city of Iguala, Jose Luis Abarca, with murder and attempted murder in connection to the missing students. According to authorities, Abarca ordered police and a gang to attack the students in order to prevent them from derailing a speech set to be delivered by his wife, reported the Los Angeles Times.

On Thursday, parents and relatives of the students demanded the suspension of the upcoming elections in Guerrero. In a letter delivered to the National Electoral Commission, they argued that the June 7 elections should be suspended to prevent people from voting for more corrupt politicians who are tied to drug trafficking, like Abarca. The four-page letter also says the violence and infiltration of gangs in politics have create an undemocratic environment for elections. As a result, the letter suggests that town councils be named by people or organizations of "high moral standards."

Meanwhile, other supporters demanded answers about the students since only one victim's remains have been identified.

"These last six months have been torture, painful, an agony for us," said Meliton Ortega, an uncle of a missing student, during the protest, according to AFP.

"We came to tell authorities and the Mexican government that as parents we cannot allow the elections," Ortega added, reports The Associated Press.

Others demonstrators held signs that read, "Peña Nieto: Guerrero demands justice, not elections."

Also on Thursday, the Attorney General's Office issued a statement defending the investigation, saying it has been "transparent, exhaustive and in accordance with the law." It also declared that government officials will continue looking for more suspects.

So far, 104 people have already been detained in the case, including 48 Iguala police officers.