Criminal Law Questions? Ask a Criminal Lawyer.
While you may sue the district attorney, it will be a very difficult case. I have no reason to doubt the sincerity of your case, but district attorneys are largely immune from suit when it comes to decisions whether or not to prosecute an individual unless there is some other wrongdoing.
You can sue in state court, but you might have better luck brining a suit in federal court for a civil rights violation.
In the interim, you can file a complaint against the DA with the state bar association, as well as the attorney general for your state.
Finally, you can file a complaint with the US Dept of Justice.
I hope this helps.