Prime accused among two were arrested over four-years-old boy Rahimul Islam Rounak murder who was found dead after two months of missing.Rangpur Kotwali police arrested the prime accused Mobashwer from Mohammadpur of the capital and his sister Ruma Begum from Savar, the outskirt of Dhaka, on Tuesday night.It is mentionable that, Rounak, son of human rights activist Mosaddek Hossain Ranga, was abducted in front of their own house of New Adarshapara area of the Rangpur City on December 1, 2015. The body of Rounak was recovered from a well of Khoragachh area of Mithapukur area on December 29.