In a breakthrough, Tabarak Ansari, the mastermind of police massacre conspired and executed by CPI-Maoist at Khukru weekly market under Tiruldih thana area in Seraikela-Kharsawan district on June 14 surrendered in the court on Monday. SP, Seraikela-Kharsawan district, Karthik S today said they would take Ansari to police remand for further probe into the case. The rebels had killed five policemen on duty at Khukru haat and fled the spot after snatching assault rifles of the slain cops.