The forensic psychiatric expertise of homicide perpetrators is a standard practice in criminal justice matters. Its validity relies heavily on the knowledge, professional experience and methodology of forensic psychiatrist experts. In the present interview, Daniel Zagury, an important figure of forensic psychiatric expertise in France, shares his clinical practice. In addition, he describes his experience with homicide perpetrators, particularly with serial killers and Islamic terrorist attackers on French soil. Finally, he addresses the recurring and crucial controversy of criminal responsibility, or the lack of it, in perpetrators.