Ostroff

Ostroff is a Russian terrorist working for Vladimir Bierko during Day 5.

Day 5
Ostroff, under commands from Vladimir Bierko, contacts Dwayne Thompkins and offers to purchase the CTU keycard that Thompkins stole from Lynn McGill. He procedes to meet Thompkins and execute him and McGill's sister Jenny. He is able to reprogram the keycard to show his face and enter CTU. Once inside he attempts to place VX gas inside the CTU air system. While in the process of modifying the airsystem, Carrie Bendis discovers his actions and walks into the room. Ostroff stranges her, killing the agent.

After placing the gas, Ostroff attempts to escape but is discovered on his way out. He is confronted and killed by Jack Bauer while attempting to draw his weapon. Bauer was too late, and the VX gas is released on CTU, killing 40% of the staff including Edgar Stiles.