North Sumatra Police have arrested an oil palm plantation owner believed to be the mastermind behind the murder of two journalists-cum-activists, Maraden Sianipar and Maratua P. Siregar.

The two were found dead with stab wounds all over their bodies in a ditch near an oil palm plantation run by PT Sei Alih Berombang, also known as the multibusiness cooperative (KSU) Amelia, in Wonosari village on Oct. 30.