Trying to test the validity of attorney-client privilege in a billion dollar securities fraud case against Walgreen Co. and two of its former officers, the plaintiffs asked Magistrate Judge Gabriel A. Fuentes to conduct an in-camera review of 75 documents that, according to privilege logs, involved: “(1) communications between non-attorney employees; (2) emails on which in-house counsel is copied and is not a sender or recipient; (3) emails disseminated ‘widely’ within the company and through distribution lists; (4 …