A businessman has been shot dead by unidentified assailants in front of a mall here, following which his woman friend was detained today, the police said. She was detained by the Kavi Nagar police a day after the incident. A case has been registered against a realtor with whom the woman was working, they said. The incident occurred last night Raj Nagar when the victim was coming out of the mall with the woman, the police said. The body has been handed over to his family after post mortem. He was shot thrice, they said. The case was registered on a complaint by the victim's father, the police said. The matter is being investigated, they added.