A protest to demand justice for 43 Mexican students who disappeared in 2014 turned violent on Thursday, injuring 11 police officers, authorities said.

A confrontation broke out outside the Attorney General’s office in Mexico City after protesters gathered demanding the arrest of people linked to the case.

“Some protesters physically attacked officers and threw explosive devices at them,” Mexico City’s Public Security Secretariat said in a statement.

“As a result, 11 police officers were injured by firecrackers and bruises from beatings on various parts of the body,” it said.

Officers were taken to hospital for evaluation and were found to be out of danger, the statement said.

Demonstrators scrawled graffiti in front of the attorney general’s office and carried banners calling for the safe return of students.

So far, the remains of only three victims have been identified.

On Wednesday, relatives of the students protested outside the Israeli embassy demanding the extradition of Tomas Zeron, a former top investigator wanted in connection with the case.

Zeron is one of the architects of the so-called “historical truth,” the official version of the case presented in 2015, which was rejected by victims’ families and independent experts.

The 43 student teachers had seized buses in the southern state of Guerrero to go to a demonstration in Mexico City before disappearing.

Investigators say they were arrested by corrupt police and handed over to a drug cartel who mistook them for members of a rival gang, but what exactly happened to them is disputed.

Last month, a truth commission charged by the current government with investigating the atrocity branded the case as a “state crime” involving agents from various institutions.

The next day, former Attorney General Jesus Murillo Karam, who led the controversial “historical truth” investigation, was arrested on charges of enforced disappearance, torture and obstruction of justice.

Arrest warrants have been issued for more than 80 suspects, including 20 military personnel, 44 police officers and 14 cartel members, according to prosecutors.