I also don't see anything wrongful about the termination. I suspect that the investigator might have been wrong even back then but if your employer bought his story and kept you on the payroll this long, count your blessings.

Here's a brief summary of wrongful termination in Illinois:

http://www.wrongfulterminationlaws.c.../illinois.htm#

Call the Illinois Department of Human Rights and the nearest EEOC Field Office and see if anybody there can shed any light on the issue.

If you aren't satisfied with those places, google wrongful termination lawyer and see what a lawyer can tell you.

Meantime, file for UI ASAP so you don't lose any benefits.