There is nothing for you on this forum other than to tell you that you need to hire an attorney immediately.
Disclaimer: I am a lawyer licensed in the State of Illinois only, and I am not your lawyer (unless you have been in my office and signed a contract). This communication is not intended as legal advice, and no attorney client relationship results. Please consult your own attorney for legal advice. This is for informational purposes only.
If you have the means to help your son obtain the services of a competent lawyer, that is the best thing you can do. These are serious charges that should not be taken lightly.
You need to retain an attorney soon as possible. If he is searious about the joining the service you might have your attorney approach the prosecuting attorney and use the military commitment to try and obtain a some sort of favorable result or plea or dismissal. Coby