Any unsubstantiated testimony of witness is not the basis for jurors to make a judgment. Because in general, it is wise to highly suspect that anyone has no evidence for litigation requests, but jurors should not trust their common experience in order to be consistent that declare the defendant guilty based on all unconfirmed confessions.
The statement 'When the defendant does commit the crime or finally believes that the plaintiff has sufficient evidence, he sometimes pleads guilty' supports the above view.