Murder on the 31st Floor (1981)

Police officer Jensen orders the evacuation of a leading media group's office building after a bomb threat is made. There won't be any explosion, however, the media group sustains big losses because of the work stoppage and the management requires investigation of the case. Officer Jensen identifies six suspects, then finds out that he is being followed himself, especially when he gets involved in the obscure activities of the mysterious 31st department.