Obviously, a scenario where the employer had credible evidence of abuse and ignored it and let the employee continued the abuse is one thing. The employer is responsible for the new victims and deserves to be punished. I'm talking about scenarios where the employer is finding out for the first time about credible allegations of abuse.
1) Don't cry witch hunt.
2) Cooperate with law enforcement completely.
3) Make every attempt to protect the anonymity of all parties until the investigation is completed. Every attempt.
4) Retrain the employee or revisit the company's code of conduct or something similar. Reinforce with the employee that this is not an implication of suspicion, just policy.
5) If you have an HR department, follow their recommendations to the letter
I'm probably missing a lot of details, but strictly following those 5 steps should save you a lot of grief.