How do routine police encounters build or undermine community trust, and how might they contribute to racial gaps in citizen perceptions of the police? Procedural justice theory posits that officers’ interpersonal communication toward the public plays a formative role, but experimental tests of this hypothesis have been constrained by the difficulties of measuring and manipulating this dimension of officer-citizen interactions. Officer-worn body camera recordings provide a novel means to overcome both of these challenges. Across five studies with laboratory and community samples, we use footage from traffic stops to examine how officers communicate to drivers and whether racial disparities in officers’ communication erode institutional trust in the police. Specifically, we consider the cumulative effects of one subtle interpersonal cue: an officer’s tone of voice. In Studies 1A, 1B, and 1C, participants rated thin slices of officer speech. Participants were blind to the content of the officer’s words and the race of their interlocutor, yet they evaluated officers’ tone toward White (vs. Black) men more positively. By manipulating participants’ exposure to repeated interactions, we demonstrate that even these paraverbal aspects of police interactions shape how citizens construe the police generally (Study 2), and that racial disparities in prosodic cues undermine trust in institutions such as police departments (Study 3). Participants’ trust in the police, and personal experiences of fairness, in turn, correlated with their perceptions of officer prosody across studies. Taken together, these data illustrate a cycle through which interpersonal aspects of police encounters erode institutional trust across race.