My advice to employees who report wrongdoing to their ethics and compliance officer: tell the whole truth.
If you leave something out, it will affect your credibility. Once your credibility is affected, nothing you said, or will say, can be taken for granted.
The ethics officer you hoped would be your partner in righting a wrong will now have to doubt you every step of the way. Furthermore, she may lose some of her appetite to fight your fight.
If some of the facts are not helping your case, you should still disclose them up front. Don’t let your ethics officer find out from someone else.