It is possible to "seal" records in juvenile cases. However, some research must be conducted to review the Court's Order. Also, it is unusual that a co-defendant would be absolved when another is not. Nevertheless, it sounds like you need to hire a lawyer to get to the bottom of this matter.
You may be able to get the charge "set aside" which is less than an expungement but you probably need an attorney in this area to look at the matter.
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