Obaidul Khan, suspected killer of schoolgirl Suraiya Akhter Risha murder case arrested in Nilphamari early Wednesday.Mashiur Rahman, Officer-in-charge of Ramna Police Station, confirmed the matter to the reporters.He said¸ a team of Ramna police station in cooperation with Nilphamari district police conducted a drive at Doba area and arrested Obaidul.Risha, 14, daughter of Md Ramzan Ali of Bangshal of old Dhaka and an eighth-grader of Willes Little Flower School and College, was allegedly stabbed by Obaidul in front of her educational institution at Kakrail in the capital on 24 August.She succumbed to her wounds at Dhaka Medical College Hospital on Sunday morning.