This paper examines defendants’ argumentative discourse in the 2008 Nigerian investigative public hearings on the Federal Capital Territory administration. The data, which consist of nine defendants’ presentations, are analyzed qualitatively, using a combination of the pragma-dialectical and extended pragma-dialectical theories of argumentation. The findings show that the hearing panel initially starts of as the institutional protagonist and defendants as the antagonists, and but later serve as the institutional antagonist and protagonists, respectively. The defendants tend to use analogy and causal argumentation schemes while employing subordinative and complementary coordinative argumentation structures. The defendants also employ different strategic maneuvers at different argumentative stages of the critical discussion. Due to the politico-forensic communicative domain and information-seeking genre of the investigative public hearing discourse, the concluding stage is suspended. Thus, the study shows the influence of communicative activity type on the argumentative activities in a critical discussion.