Interpreting in a legal setting in Ireland is not subject to any regulation. Police and court interpreters are neither certified nor tested. The current study aims to analyse the impact on a criminal trial of unqualified interpreters’ assistance in the pre-trial process. The starting point of the investigation is an analysis of witness statements written with the assistance of unqualified interpreters. It is followed by an analysis of the statements’ translation into Polish. The analysis of statements is performed based on Juliane House’s translation quality assessment model. Finally, analysis of court transcripts investigates the impact of translation and interpreting on the trial. The findings show that covert translation of witness statements disrupts the flow of the trial and suggest that overt translation may be more appropriate for this text type. The investigation highlights the dangers related to commissioning unqualified interpreters and translators in a legal setting and confirms an urgent need to regulate this field in Ireland. Furthermore, the study demonstrates that Juliane House’s translation quality assessment model can be successfully applied to legal texts such as witness statements.