Part III Investigative interviewing | Section II Initial preparation 4. USING POWERS AVAILABLE TO COMPEL TESTIMONY In certain circumstances, any powers of subpoena that are available to the NHRI may have to be used to compel otherwise reluctant witnesses to give evidence. A “friendly subpoena” may also be served. This occurs in cases where someone is quite happy to give evidence but is concerned about potential retaliation or the perception of others, should they be seen to do so voluntarily. The person served with the subpoena can then legitimately claim that they have no choice but to be interviewed by the NHRI. 5. TAKING EVIDENCE UNDER OATH Some NHRIs may have the power to take evidence under oath or affirmation. Normally reserved for formal hearings, it is a tool rarely used in field investigations. However, it may be worth considering in some situations, particularly where there are concerns about credibility. If sworn testimony is going to be taken for only one or two witnesses in an investigation, the interviewer must be in a position to explain why only certain witnesses were required to do so. In those circumstances, it may be worth considering interviewing all witnesses under oath. UN Photo by Fred Noy. Chapter 11: Logistics and other special considerations | 69