Turkish authorities arrested three people over the death of a Syrian filmmaker who was assassinated in southern Turkey after producing anti-Islamic State documentaries, the state media said Sunday.

Naji Jerf, 37, was shot dead in broad daylight in Gaziantep province late December by assailants using a silencer outside a building that houses Syrian opposition news outlets.

A court in Gaziantep remanded in custody pending trial one suspect and his two accomplices, the official Anatolia news agency said. There were no other details on their identity.

Jerf was the editor-in-chief of a Syrian magazine, Hentah, and had recently directed and produced a documentary about the killing of Syrian activists by IS jihadists.

He was also an activist in Raqa is Being Slaughtered Silently (RBSS), a group of citizen journalists who work to expose human rights abuses in Raqa, the northeastern city that IS uses as its de-facto capital in Syria.

This is not the first time a Syrian opposition figure has been murdered in Turkey.

At the end of October, IS claimed responsibility for killing of young activist Ibrahim Abdelkader and his friend Fares Hamadi.