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Your situation is troubling but not uncommon unfortunately. HR does have an obligation to investigate all claims that are submitted. Clearly this person has had multiple complaints but for whatever reason they seem reluctant to act. I am concerned for you for speaking on other employees' behalf. While your heart was in the right place, what is likely to happen is that those employees will deny it and now it looks like you made it up (even if that is untrue.) Now, you could be fired with cause for making false statements (allegedly).
I think that helps but I would focus on your concerns primarily.
Sorry to be clear you could be fired but I think you would have a strong claim against them. What I was saying is focus on your concerns and issues. Do not try to speak for others