BOGOTA, Colombia (AP) — A student leader who lost an eye in clashes with police in 2018 and also participated in anti-government protests that swept over Colombia in April and May was slain in the southwestern city of Popayan, local police reported.

Esteban Mosquera was an advocate of free tuition for university students and also campaigned in his hometown of Popayan for a basic income plan for Colombia’s poorest residents. Witnesses said men on motorcycles shot him as he walked toward his home Monday.

The Interamerican Commission on Human Rights urged Colombia’s government to promptly investigate the killing, while President Ivan Duque offered a $13,000 reward Tuesday for information leading to Mosquera’s killers.

So far this year, 108 human rights activists and community leaders have been slain in Colombia, according to Indepaz, a human rights group that notes violence against activists has increased since the Revolutionary Armed Forces of Colombia signed a peace deal with the government in 2016 and disarmed. It said more than 300 activists were killed last year.

Jose Miguel Vivanco, the Americas director for Human Rights Watch, expressed regret over the slaying of Mosquera, saying on his Twitter account that Colombian authorities must “shed light” on the homicide and “prosecute those who are responsible.”

In 2018, Mosquera, who was a music student, lost his left eye during a protest when he was hit by a projectile launched by police, but he continued his political activism.

When demonstrations over a proposed tax hike broke out last April, Mosquera joined in and also produced reports on the protests for a local website as well as social media videos calling on Colombians to join the protests.

The protests raged almost daily for two months and saw at least 58 people killed, but the demonstrations have since dissipated.