The experiments involved interviews of police officers and students, individually or in connection with questionnaires and free recall that was computed according to ratings of confidence, accuracy, completeness, implicational errors, and confusing errors. Overall the results showed that collaborative testimonies exclude potentially useful information. Thus, if one member of the group represents the group testimony, the written report is used not to refresh the memory but as a substitute for memory. Therefore, individuals should be required to take personal responsibility for their testimony. In addition, statements by several witnesses would lead to a greater completeness of the joint testimony than would a statement by only one witness. Collaboration of police officers should not be excluded in the recording of evidence, but the subsequent evidence of two individuals testifying as individuals can reveal more than is contained in the collaborative statement. Figures, tables, and 20 references.