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.
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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.