How does a whistleblower prove retaliation?

There are many ways for a corporate whistle blower to prove retaliation. One, did the employer offer an untrue explanation for the adverse action? Number two, is there evidence of animus? Did the employer resent that the employee blew the whistle about that issue? For example, would the employer have to spend a lot in order to address or to remediate the employee's concerns? Three, is there evidence of unlawful retaliatory motive? Four, is there evidence that the employer's explanation has altered at various stages? For example, did the employer claim one reason when the adverse employment action happened but when they go all the way to the hearing, they offer the opposite reason or explanation?