My name isXXXXX am a licensed attorney and am glad to try and answer your question.
I am honestly sorry for your son's circumstances and commend you for wanting to help.
Accordingly, I'm pleased to say there is a solution here. Based on your description of events, the most likely causes of action would be for both state law torts (against the bouncers and their employers) as well as a federal civil rights case (against law enforcement) pursuant to 42 U.S.C. § 1983. To see if your son has viable grounds for filing suit, he must have his case screened on the merits by a plaintiffs' trial attorney. If an attorney accepts the case pursuant to the customary contingency fee agreement there would be no up-front charges to your son. Rather, his legal counsel would only get paid out of the proceeds of a verdict or settlement if he or she were successful in obtaining a favorable outcome and winning the case on your son's behalf.
This can only be done through having a lawyer review your circumstances, meaning it cannot be done in this online informational venue. In other words, you have done all you can do, your next step at this juncture is to confer with legal counsel, but the good news is that process is entirely free of charge to you. I can only imagine what a stressful and trying time this is for you, so please believe me I mean it when I say I am glad to say there is a way to seek justice without having the burden of trying to pay attorneys' fees .
To help folks in this online venue, I am required to follow site rules including refraining from accepting cases and/or making direct referrals to named attorneys. However, I can tell you where I would turn were I in your very shoes. Toward that end, my very next step would be to take advantage of the resources of the non-profit, American Bar Association accredited, National Board of Trial Advocacy Division of the National Board of Legal Specialty Certification. Here is a listing of all such Board Certified Civil Trial Advocates practicing in the applicable jurisdiction (please just click the following link):
If you have a follow-up question or need clarification, please just say the word by using "reply" to reach me.
I truly hope all works out for your son.