You can't sue the police officer if he was acting within the letter of the law, which in this case it sounds like he was.
You can't sue Thomas, what are you going to get out of it?
What you need to do is contact a lawyer who can help cut through the red tape and advise about a possible name change.
If your son isn't driving and has no plans on it, and his license has expired, then have him go to DMV and just "cancel" it and get a state issued ID card for himself. That way if Thomas tries that one again, he'll get hauled in for driving without a license.
And if it was me, and I got a summons for a crime I wasn't at all involved in, I'd be calling the court clerk in the morning and telling them that I had my identity stolen by Thomas in the past--look up the court records, and that I wasn't going to waste my time or energy dealing with it any further. Come get me, and better have the DA there to be served with false imprisonment papers by my lawyer. But I hate courts, school districts and authority figures in general, so that's just me.
Seriously, time for a lawyer. I know a few decent ones who deal with criminal law, let me know if you want a referral. (One has Saturday morning office hours and will deal with the client via e-mail if that's better for your son.)
One thing the lawyer can do is pressure the DA to look into this mess and possibly have Thomas picked up for identity theft, criminal impersonation, and obstruction of justice. At this point the gloves are off. Or you could just shoot him. (Just kidding...maybe

)
Anne