<div>The 1999 Columbine High School shooting was a bold reminder which emphasized the importance of active shooter preparedness for the first responder communities and the general public. Since Columbine, the preparedness for active shooter incidents (ASIs) both in the public and private sectors proactively took place. Currently, the RUN.HIDE.FIGHT.{\textregistered} (RHF) response for unarmed individuals is implemented as part of the emergency response throughout the United States. Despite the RHF's nationwide implementation, there is a lack of literature that supports the effectiveness of RHF to lower casualty rates during ASIs. </div><div></div><div>This thesis examined casualty differences of RHF and the shooters' discharge interval by creating the incidents that have occurred in the library during the 1999 Columbine High School shooting with AnyLogic's agent-based modeling capabilities. Recreating ASI in a virtual environment naturally removes the participants’ physiological and psychological implications. Additionally, the flexibility of agent-based modeling allows validating the model based on the historical events than to run various what-if scenarios. The outcome of this thesis examines the effectiveness of RHF by comparing the output data from the actual event to models with RHF implementation.</div>