The criteria used by Swedish courts for assessing credibility of plaintiffs' accounts were for the first time scientifically evaluated. Furthermore, unlike much previous deception detection research, we used offenders as participants instead of college students. False and truthful confessions by 30 offenders were analysed, and few significant effects were obtained. Truthful confessions were rated as having a higher degree of clarity than false confessions. Women's truthful confessions were rated as more credible than their false confessions. The offenders who were most experienced in being interviewed by the police gave a stronger impression of talking about something self-experienced in their false than in their truthful confessions; hence, it seems that offenders with more police interview experience have developed a kind of expertise in telling a convincing lie about crime. Overall, the criteria for credibility assessment used by Swedish courts had very limited usefulness in discriminating truthful and false confessions. A critique of the current status of evaluating statements in Swedish courts is provided.