We do keep their identities confidential even though they have to identify themselves to us. Because if it's an anonymous letter, it means we can't verify the information with anybody, other than going to the organization, so the act says that we'll protect the identity of the discloser to the extent possible.
Number one, they might come to us because maybe they've raised the issue internally and they weren't satisfied with the results. Or they might come to us because it's a small organization and they fear being identified. Also, they might come to us as we're an independent organization. In fact, I've even had suggestions from leaders of the organizations that they might want us to investigate the matter to ensure that it is completely at arm's length and is seen as fully independent.
That's the way the act was constructed.