Using some of the best ways you know of to build rapport with someone you are interviewing, should the techniques be any different for different kinds of interviewees such as witnesses, victims, or suspects?
This question is difficult to answer as building rapport or mutual respect and a sympathetic relationship is different for most people and circumstances. The usual ways to build rapport can be eye contact, a pleasant voice and demeanor, allowing the person to initiate contact such as a handshake, talking about the weather or some other innocuous subject to allow them time to relax, or giving them space to relax. Without question, the techniques vary if the person is a witness, a victim, or a suspect. Each person is in a different position as an interviewee, so the person must be approached differently. The skill of the interviewer determines which techniques will work best with the interviewee depending on shyness, fear, mental illness, anger or rage, or previous contacts with the law. As a volunteer on-call crisis counselor for a county jail, I need to establish rapport within the first five minutes or I can't really get any further.
For me, speaking quietly and sitting further away for personal space are important. A loud voice and ordering interviewees often results in complete failure if tried. I get much more information if I let them talk and lead the discussion with a few prompts from me. Giving them an example of something about me, carefully stated, which is like them, helps them see me as less threatening. On the other hand, if this person was a suspect, I would never give them information about myself, but try to find something we could both talk about such as sports or tv shows etc.
Mentally ill people need to be informed what I am going to do such as move closer before I do that or allow them to decide if they are comfortable with me moving closer. Space, voice volume and eye contact are important with them.
There is no one magic technique which works to establish rapport, but it does require an observant person who can see the reaction their questions produce and adjust their interview accordingly, especially if the interview subjects are a witness, a victim or a suspect.