Previous studies have addressed many different kinds of confessions in police investigations – real, false, coerced, fabricated – and highlighted both psychological and social mechanisms that underlie them. Here, we focus on inadvertent confessions and admissions, which occur when a suspect appears to be confessing without being fully aware of doing so, or when police officers believe they have a confession or admission of guilt when in fact this is not the case. The goal of the study is to explain when, how and why these confessions and admissions occur as well as how they are dealt with in two different jurisdictions, the United States and the United Kingdom. We use a discourse analysis approach because inadvertent confessions and admissions of guilt are the product of miscommunication – they happen because the speaker’s meaning and the hearer’s meaning are misaligned. The data consist of 50 interviews from the United Kingdom and 50 interrogations from the United States with both English-speaking and non-English speaking suspects. Our results demonstrate that inadvertent confessions can occur in both locales due to reliance on inference, which is inevitable since inference is the backbone of any human communication, as well as due to additional factors such as linguistic, cultural and procedural issues. We found that these phenomena are more frequent and less well controlled for in the United States context due to (a) no systematic checking of understanding, (b) adversarial questioning techniques and an absence of legal representation, and (c) lack of professional, high-quality interpreting. We discuss the implications of our findings for current efforts to improve access to justice, custodial procedures and language services, and we make recommendations for the implementation of our research in professional practice.