Ann Kiernan replies:

In a 1995 decision, the U.S. Supreme Court said no. Fearing that her employer would fire her because she was 62, a worker gained access to and copied several of the employer's confidential documents. When she was fired as part of a claimed reduction in force, she sued for age discrimination. During pre-trial discovery, the employer learned that she had copied its confidential records, so it sent her another termination letter, stating that she was discharged for misconduct.

The Supreme Court ruled that the so-called "after-acquired evidence" of wrongdoing, which would have resulted in discharge if discovered earlier, did not bar the worker from relief. The law, after all, was intended to eliminate discrimination in the workplace. If age was the basis for her discharge, said the Court, she was entitled to damages that included back pay up to the time the employer learned of her misconduct.

McKennon v. Nashville Banner Publishing Co., 513 U.S. 352 (1995)

Thus, the after-acquired evidence rule may prevent a wrongfully-discharged worker from recovering much in damages, but does not prevent a lawsuit.