H. had perceived his father as an evil persecutor ever since his adolescence. He developed paranoid schizophrenia of persecution in which his father occupied the main role. Little by little, in his desperate resistance against his father, perceived as his enemy, he acquired such a feeling of prejudice, of violation of his personality, and of impotence that the only way out was to escape in order to survive. At the age of 18, he decides to run away from home and from France to stop suffering. He goes to Canada and later to the USA where he would stay 9 years, during which his madness does not stop. Wherever he goes, he always feels the presence of his father in his head: "He orders me, he criticizes me from a distance, he steals all my thoughts, he is in charge of my actions, he takes away the bread from my mouth to humiliate me and kill me…" Thanks to his marginal lifestyle, he maintains a relative adaptation, a fragile equilibrium in his existential bubble in which he doesn't tolerate any breaking and entering. His delusion of prejudices and persecution, of which the main character had always been his father, extends to include society in general, cornering and leading the subject to commit an offense as a reaction of irrepressible pathological self-defense. He is questioned by the police, taken to prison and later taken to an American psychiatric hospital, after shooting at those whom he thinks are "CIA agents" (who are actually people forcing him to move the boat in which he lives). After being deported back to France, he returns to his parent's home, the source of all his madness. During the following months, he lives locked up in his room afraid of being near his father and tormented by his delirious ideas. In order to stop his suffering, he decides to buy a fire-arm to kill himself. One day, his father, accompanied by his mother, break into his room. He takes the rifle hidden under the mattress, and kills his father at point blank. "I thought that I had instantly killed my father, because he fell face down on the ground. On the other hand, my mother remained standing while my sister, screaming, escaped through the window of the living room. My mother, injured on her right side, moved back to the living room. Seeing that my mother hadn't fallen to the ground and not wanting to make her suffer, I reloaded my rifle. I took out the cartridge, and reloaded the rifle with a cartridge of buckshot. It seemed to me that she was still standing in front of the couch. I fired the gun a second time without looking and at that moment she falls on the couch… dead… She is the enemy because she is my father's wife".The recounting and analysis of this double psychotic parricide case illustrate the psychopathologic constants and criminal dynamic that are most often present in this type of crime. The constants are the following: the perpetrator of the post-adolescence or adult parricide is often a psychotic young man; he/she lives a long, delusional story in which one or both parents have an important role; this insane delusion leads to suffering and/or to identifiable behavioral problems that together can constitute a criminal psychic state; The homicidal reaction takes place right after one or a group of factors (such as an argument, brawl, a fit of delusion, interruption of the therapeutic treatment…) that are set off in the criminal pathological state. These psychopathological constants, if they conjoin, are also the factors and indicators of danger. They should be considered as a warning sign to take preventive and remedial measures.