De-identified or anonymous?
Anonymous means the sender of the report is not known. You cannot ask for more details or verify certain statements. That is not good.
De-identified means the sender of the report is known and available for further clarifications, but his identity is never revealed during the investigation process. This is important to safeguard, even if the identity of the person involved is ‘obvious’ or ‘everybody knows this’. Do not reveal. Never. Not even whether it was a he or a she that was involved. This will install trust with the reporters that is crucial for a good reporting culture.
Breaking the confidence may mean you have received your last report!