From United States v. Capital Tax Corp., 2011 U.S. Dist. LEXIS 13242 (N.D. Ill. Feb. 10, 2011):

The challenged interrogatories and document requests ask the government to identify, among other things, each person who made decisions regarding whether to name Dukatt in this case, the dates on which those determinations were made, and any documents relating to those decisions. *** The government objected to these interrogatories on the grounds that they are "protected from disclosure by the attorney work-product and/or attorney client and /or deliberative process privileges," *** and to the document requests on the grounds that it had "produced all responsive, non-privileged documents as initial disclosures" ***. Dukatt argues that the government's assertion of privilege is overly broad because, according to him, it covers objective facts that represent details of the information it has already disclosed to the district court in pursuing its equitable estoppel theory at the motion to dismiss stage.

Although Dukatt is correct that the work-product and attorney-client privileges do not extend to underlying objective facts, see Diemer v. Fraternal Order of Police, Chicago Lodge 7, 242 F.R.D. 452, 458 n.9 (N.D. Ill. 2007), a party may not ask about the identity and knowledge of people with respect to relevant facts "in a fashion that effectively infringes upon the opposing attorney's preparation of the case for trial," Board of Educ. of Evanston, Twnsp. High Sch. Dist. No. 202 v. Admiral Heating & Ventilating, Inc., 104 F.R.D. 23, 32 (N.D. Ill. 1984). Thus a party may ask, for example, who has been interviewed and what they said in the investigation phase of a case, but an interrogatory seeking the identity of the attorney who conducted the interview may cross the line into protected work product. See EEOC v. Jewel Food Stores, Inc., 231 F.R.D. 343, 347 (N.D. Ill. 2005) [approving interrogatory that asked: “Identify. . . each person from whom Defendant has obtained a statement, affidavit or the like, written or otherwise, concerning any act, circumstance or event related to any claims or defenses in this case and for each such statement provide the substance of the statement and identify the custodian thereof”]. Here, the challenged interrogatories and document requests are designed to delve into the government attorneys' preparation of the case. For example, in interrogatories 7, 8, and 11 Dukatt requests the identity of the attorneys who participated in the decision that there was no basis to pursue him as an owner in 2006. Those requests are specifically linked to Dukatt's request that the government produce the documents and information the identified attorneys relied on to make the determination. *** Dukatt also asks for a description of the nature of the role of each of those attorneys in deciding who to sue and when. *** Although Dukatt has carefully framed those requests as inquiries into mere identities and dates, such information is relevant only to the extent that it serves as a crowbar to pry open a window into the strategic thought process of the government's attorneys. But as the government argues, those thought processes are protected by the work-product doctrine. See Sandra T.E. v. South Berwyn Sch. Dist. 100, 600 F.3d 612, 621-22 (7th Cir. 2009)