Hello and thank you for entrusting me to assist you. My name is ***** ***** I will do everything I can to answer your question.
The general rule in South Carolina is that employment is "at will" absent an express agreement to the contrary. At will employment can be terminated or suspended for any reason not amounting to discrimination on the basis of a legally protected trait (race, religion, gender, etc.) or retaliation for engaging in certain forms of legally protected conduct (filing a wage claim, taking FMLA leave, etc.). It doesn't matter whether the basis for termination/suspension is fair, reasonable or even true.
Unfortunately, this means that there is nothing unlawful about an employer putting an employee on administrative leave due to an allegation of stalking/harassment. This remains the case even if there is never an arrest and even if the allegation is proven to be completely untrue. Again, since employment is at will, employers don't need to justify their reasons at all and so a bad reason will still not violate the law.
As for allowing the agent to question you on the job, there is nothing unlawful about that as your employer owed you no legal duty to protect you from the investigation.
I hope that you find this information helpful and am genuinely sorry if it is not what you were hoping to hear. Please do not hesitate to let me know if you have any questions or concerns regarding the above and I will be more than happy to assist you further.
If you do not require any further assistance, please be so kind as to provide a positive rating of my service so that I may receive credit for assisting you. Very best wishes moving forward.