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Alejandrino Gonzalez, Associated Press
An emergency worker tries to extinguish a burning passenger van after protesters set it ablaze in the city of Chilpancingo, Mexico, Thursday, March 26, 2015. Protesters marked the six-month anniversary of the disappearance of 43 students with marches in Mexico City and other cities in Mexico and asked that elections scheduled for June in the southwestern state of Guerrero be suspended. Federal investigators say local police handed the students over to a drug gang, which killed them and incinerated their remains. Nearly 100 people have been detained in the case.

MEXICO CITY — Parents of 43 missing students marked the six-month anniversary of their disappearance Thursday by marching to the federal elections office in Mexico City to ask that voting scheduled for June in the southwestern state of Guerrero be suspended.

Dozens of protesters, including some of the missing students' parents, delivered a letter to the office asking that the June 7 elections not move forward because people could be voting for politicians tied to drug trafficking, as was the case with former mayor of Iguala, Jose Luis Abarca, who remains in custody.

Parents and their supporters later staged a protest march in the capital, while small bands of activists defaced campaign posters and burned a small bus in the Guerrero state capital of Chilpancingo.

The students from a rural teachers college were last seen in Iguala. Federal investigators say local police handed the students over to a drug gang, which killed them and incinerated their remains.

On Thursday, the Attorney General's Office issued a statement reiterating that the government had conducted a transparent and exhaustive investigation. It said 104 people had been detained in the case, including 48 from the Iguala police force.

Only one victim's remains have been identified, however, and parents of the young men have continued to demand answers about the events of Sept. 26.

"We came to tell authorities and the Mexican government that as parents we cannot allow the elections," said Meliton Ortega, parent of a student. "They have been six months of torture, of suffering for us."

Students from the Rural Normal School at Ayotzinapa went to Iguala on Sept. 26 to collect money and hijack buses, a common practice, so that they could attend events in Mexico City. But police confronted them in Iguala, firing on the buses. Six people were killed.

Federal investigators determined the police turned the students over to members of a drug gang who took them to a remote garbage dump near the town of Cocula, killed them, burned the bodies and threw the remains into a river.