Whether or not it is your employer's regular procedure to put employees on paid leave when it investigates is up to your employer. The law does not have any requirements either way.
However, if it is not your employer's regular procedure to put employees on paid leave when it investigates, then you may have a viable grievance against your employer. In that scenario, it would seem that you are the victim of retaliation. This is because other employees in your situation are treated differently.
On the other hand, if your employer puts all employees on paid leave when it investigates, then you would not likely have a viable grievance. This is because you would be treated the same as all employees are treated in the same situation. Accordingly, it would not seem that you are the victim of retaliation in that scenario.
So, the bot***** *****ne is that whether or not you were the victims of retaliation likely depends on your employer's ordinary procedures and policies with regard to similar investigations. You may wish to speak to the HR department to find out what they ordinarily do. If they do not ordinarily put people on leave in your situation, you may wish to speak to a local employment attorney who can inquire directly to your employer and take legal action if necessary.
Does that answer your question? Please let me know if you need clarification, as I am happy to continue helping you until you are satisfied.