The Third Killer is just a theory and never proven. The killers had partners in Scream 1 and Scream 2. However, after their revealing, many questions have gone unanswered, as it appears that both killers could not have been able to commit certain acts, either due to their presence being known or inability due to what we may know about them. As a result, many fans believe there may be a third killer throughout the Scream franchise.