A large number of students of Delhi University on Wednesday held a protest march in the national capital demanding arrest of the killer of a 21-year-old girl, who was shot dead outside her college. Holding placards, the students marched from Ramlal Anand College in South Campus of Delhi University to India Gate. RadhikaTanwar, a second-year degree student, was killed outside the college in Dhaula Kuan's Satya niketan area on Tuesday by an unidentified man.