Retaliation for report to Internal Audit

I have recently been fired for very trivial reasons, after a period of two months of hostility from my boss, which started very shortly after I reported an issue relating to his management of a project.

My former employer is a public company that recently implemented payroll and accounting systems. I raised concerns with Internal Audit that my boss was allowing that project to be completed without adequate security. Such issues would contravene our SOX 404 controls, and exposed employee confidential information to other non-employees of the company. Indeed, as of today, those issues still exist and the system is live.

Prior to this report, my boss had repeatedly reassured me that my work was good and that if he had issue, he would tell me.

However, in the following two months after the report to Internal Audit, I suffered a series of incidents where things I said were deliberately misquoted to other executives. I believe this may have been an attempt to discredit me in these executives' eyes. Projects that had once been deemed "satisfactory" were now being scrutinized (perfectly legal, I know), and a incident of coaching - where my boss told me to be careful when I talk to Internal Audit, as they were "out to find fault" with him - occurred. He also started avoiding me, not returning my calls, or responding to my emails.

The final incident came when I was terminated, again being misquoted as threatening legal action against a vendor, when in fact I was only indicating that we would not want to sign a legal agreement that would limit our ability to sue.

Is this retaliation? If so, what recourse would I need and what evidence (apart from my notes of the incidents) would I need to provide? I am not keen to return to the company at this stage.