It is not a good idea to execute a criminal human, because if he or she is dead, the criminal spirit can simply rob a baby to reincarnate in a new life. If he/she does that, than she/he can remember the last lives and directly knows how do crimes without to be easy caught. But in the time he/she is in the jail he/she cannot do any crimes outside of the jail. Additionally, if she/he is a very long time in the jail she/he may forget a lot and also her/his information how to commit crimes without being caught might out date, and because of that he/she might be caught way easier if he does new crimes even in the next life.