Police interview interpreting is a complex task, as interpreters make difficult choices under pressure and time constraints. The main dilemma of the interpreter is whether to remain faithful to the original text, with the risk of rendering non-idiomatic translations, or to give preference to more idiomatic versions that may entail an addition or an omission from the original text. This article presents an analysis of Spanish-English bilingual police interviews in California. The analysis is based on the discrepancies found between an interpreter present in the interrogation and a control interpreter who translates the whole interview post-hoc. This is an original methodology that can be used for future research in this and other contexts. The results show different types of inaccuracies in the interpretation, which can be attributed to contextual pressures and overall challenges of interpreting and to challenges related to typological differences between the two languages involved.