During violent conflict, governments may acknowledge their use of illegitimate violence (e.g., noncombatant casualties) even though such violence can depress civilian support. Why would they do so? We model the strategic incentives affecting government disclosures of illegitimate violence in the face of potential NGO investigations, where disclosures, investigations, and support are endogenous. We highlight implications for the analysis of conflict data generated from government and NGO reports and for the emergence of government transparency. Underreporting bias in government disclosures positively correlates with underreporting bias in NGO reports. Furthermore, governments exhibit greater underreporting bias relative to NGOs when NGOs face higher investigative costs. We also illustrate why it is difficult to estimate negative effects of illegitimate violence on support using government data: with large true effects, governments have incentives to conceal such violence, leading to strategic attenuation bias. Finally, there is a U-shaped relationship between NGO investigative costs and government payoffs.