It is real that no one chooses a craft: in fact, a craft, whatever could be this, chooses man. And, through the craft he defines his personality expressing himself. But, what if a man doesn't have a craft, so is he unable to express it? Or sex can replace a craft?
In art, artists just don't express themselves through their art, and it seems that these need different means to exposure their concepts or ideas, above all, themselves. Sex is the primary and primitive one of these?
Art or Sex mirrors the need of a man to express himself either through creativity or the most primitive self-expression as sex, and in some cases none of these means are enough to satisfy his urge for expression, and he has to recur to murder.