TL;DR
-----

Is it ever appropriate to raise with HR that a colleague has made (subsequently disproved) accusations against colleagues in past workplaces?

Background
----------

A manager at my company (let's call him manager X) has been accused of a serious breach of workplace policy (bullying) by Employee A, who reports to Manager X. If proven, the accusation would likely result in immediate dismissal of Manager X and would permanently damage his career.

I am aware of the issue after a HR representative queried how my interactions with Manager X had gone. I don't report directly to Manager X but have occasionally worked on projects run by him. In my experience, Manager X is a regular mid-level manager and hasn't demonstrated any behaviours that resemble bullying. The HR representative noted that the issue was particularly difficult to resolve because the accused bullying *only occurred when no one else was around.*

By chance, Employee A and I worked at another company a few years ago, again in different teams. In that company Employee A made very similar accusation against **two** of his successive managers. In **both** instances formal investigations were completed which exonerated the accused managers. This was possible because of statements from colleagues who said that Employee A grossly exaggerated events *and* other events could not have taken place because people were in different cities at the time. Employee A left the previous company shortly after the second accusation was dismissed.

Question
--------

Is it appropriate to mention to HR my knowledge that Employee A has a history of making similar accusations against their manager given:

* I've been asked by HR to comment on my experience in dealing with Manager X and nothing else.
* I have no evidence to *disprove* what Employee A is now claiming about Manager X.
* While I believe the investigations that took place at the previous company were thorough and unbiased, I have no evidence to confirm that.
* **BUT** in the absence of any third-party information (just what Manager X and Employee A say), I have no doubt that Manager X will be dismissed "just to be on the safe side", which information relating to Employee A's past behavior may prevent.