The purpose of this research was to test whether delay between a mug book task and a lineup task moderates a simple mug shot exposure effect. Following the witnessing of a simulated theft, participants searched either a small, large or no mug book. Participants then viewed a lineup that contained either the perpetrator or an innocent replacement; the lineup occurred either immediately after viewing the mug book or 48 hours later. There were fewer suspect identifications and more lineup rejections in the mug book conditions than the no mug book control; this was explained in terms of the criterion for making choices carrying over from the mug book to the lineup. There was qualified support for delay moderating the mug book exposure effect.When there is no suspect in a criminal investigation, eyewitnesses to the crime are sometimes asked to view a mug book. Mug book searches involve viewing large numbers of mug shots of individuals who have been booked in the past. At a later stage of the investigation when a suspect has been found (based on evidence that may or may not have come from the mug book search) eyewitnesses are typically asked to view a lineup. There has been considerable research directed at the question of whether the earlier mug shot viewing actually interferes with the lineup performance. A recent meta-analysis of over 25 years of research on this topic found that it does (Deffenbacher, Bornstein, & Penrod, 2006). Deffenbacher et al. (2006) concluded that mug shot exposure decreased correct identifications of the perpetrator and increased false positive identifications of innocent lineup members. In spite of this summary conclusion, Deffenbacher et al. (2006) suggested that the mug shot exposure effect is moderated by which of three types of effects was being investigated.Two of the three types of mug shot exposure effects are tested in designs in which a particular mug shot appears in both the mug book and the lineup. A transference effect involves a witness viewing an innocent individual in a mug book and then falsely identifying that person in a lineup due to transferring the memory of the innocent individual to the memory of the perpetrator. The somewhat similar commitment effect involves a witness who actually chooses an innocent individual in the mug book and then chooses this person again in the lineup due to a commitment to the earlier mug book choice. In contrast to tests for transference or commitment which both involve an overlap between a picture in the mug book and a picture in the lineup, a third type of mug shot exposure effect does not involve any such overlap. Deffenbacher et al. (2006) noted that a design in which there is no overlap between mug book and lineup resembles the classic design used by experimental psychologist to test for retroactive interference effects. The retroactive interference prediction applied to mug books is that viewing mug shots causes a retroactive interference with the memory of the perpetrator; the weaken memory results in a decrease of correct lineup ide...