In traumatic incidents such as the Columbine High School shooting (USA) in 1999; the Virginia Tech shooting (USA) in 2007; the Kauhajoki School shooting (Finland) in 2008; and the Utöya shooting (Norway) in 2011, police officers were faced with active attacker scenarios. Intervening in such ongoing events might be life threatening for the police officers involved, but may also be imperative for saving the lives of the victims. Incidents that evolve into large-scale killings are still rare (Greenberg 2007). However, what is less publicized is that regular police officers are frequently placed in threatening situations where immediate action needs to be taken under very uncertain conditions to save lives, like when someone screams out in terror from within an apartment. The danger involved in these and other police officer tasks is illustrated by the figures presented by Meyerhoff and colleagues: between 1989 and 1998, 682 police officers were killed in the line of duty in the United States (Meyerhoff et al. 2004). Hence, recent events highlight the importance of training regular police officers to handle rare but highly straining situations, where high psychological stress is commonly an associated component, since regular police officers are often the ones first to respond. Special Weapons and Tactics (SWAT) teams have the benefit of regular training, numbers, and better information, but SWAT teams generally arrive after regular police officer patrols to the scene and therefore often respond to contained situations, usually with a barricaded armed criminal with or without hostages.