If an internal investigation reveals that the employee whose complaint launched the process was also engaged in improper behavior (or was, in fact, the person to blame for the situation), don’t hesitate to punish appropriately.
As long as you act in good faith, a court is unlikely to conclude the punishment was retaliation for complaining in the first place.
Recent case: Veronica Alvarez worked as a part sorter and had trouble with a co-worker who slapped her buttocks regularly.
Alvarez finally complained to her supervisor, who reported her complaint up the chain of command. HR launched an investigation and interviewed Alvarez and the co-worker, plus others working in the same area.
Based on interviews, the company concluded that both Alvarez and the co-worker had engaged in behavior prohibited by company rules. In fact, the co-worker insisted that it was Alvarez who introduced him to the buttock-slapping game and made sexual comments directed at him. Other witnesses supported his version of events.
When the company suspended them both, Alvarez sued. She said her suspension was retaliation for complaining about sexual harassment, and that if she hadn’t initiated the complaint, she wouldn’t have been punished.
The court didn’t buy her argument. It reasoned that accepting her theory would mean that anyone who filed a complaint got immunity from punishment no matter what the investigation revealed. (Alvarez v. Des Moines Bolt Supply, No. 09-1465, 8th Cir., 2010)