Folie à deux Psychosis of killers

Kouider and Medouni exhibited symptoms of the psychosis folie à deux, or madness of two, which also affected Ian Brady and Myra Hindley, the Moors murderers.

In this disorder, a dominant character (Kouider) forces a warped view of the world on a partner (Medouni).

Criminology professor David Wilson, of Birmingham University, said: “The couples are often socially inadequate and don’t get exposed to people who may challenge their view.”