In that case, the criminal was his younger brother, and the victim was his daughter. Learning that his brother had hurt his daughter, Carl felt tortured and made some extra effort so that his brother could be kept in prison for the rest of his life.
When he learned what had happened, he proposed to call the police immediately. After he called the police, Bill was arrested. He also contacted some of his old colleagues to do further investigation. They managed to find some evidence of other crimes, like embezzlement, which was enough to sentence him to life imprisonment.
He never denied that he was merciless to his brother. But...