An Islamist militant, believed to be the mastermind of a failed assassination attempt on a Hindu lecturer in southwestern Bangladesh, has been arrested from the national capital, police said on Friday. Khaled Saifullah, who masterminded an attempt to murder Ripon Chakrabarty, a Mathematics lecturer at the Nazimuddin Government University College in Madaripur, was arrested by police’s counter-terrorism unit from Dhaka’s Demra on Thursday.