Toyo Keigo reasoning series 04 Why did Reiko Kobayakawa kill that man?

Because Reiko Kobayakawa is a bad girl with a twisted mind, she wants to get rid of her best friend's boyfriend. It seems that she is being used, but in fact she is pretending to be used in turn. Killing was her first thought. After the incident, in order to avoid criminal responsibility, she pretended to have a split personality and pretended to be a good person to defraud a lawyer for her sympathy.