Once the police and prosecutor are involved it is out of the hands of BF. The BF is only a witness and the local prosecutor representing the state handles the case. If a law has been broken it's up to the prosecutor to uphold the law and charge the GF. Saying that, most prosecutors I know are overworked and underpayed and would be happy to dismiss a Mickey Mouse case like this. The BF should write a letter to the prosecutor asking that the case be dismissed. If the BF, who is the victim is uncooperative with the prosecutor, the prosecutor may just dump the case.