Determining a "baseline" refers to the interrogator's observation of the witness's non-verbals as far as triggers and reactions. When interrogations start, the agent often starts off very passive, eliciting all sorts of verbal and non-verbal activity in the witness. A trained interrogator is able to pick up on what the typical or inherent behaviors are in each separate witness. That is the "baseline" behavior, or in other words, the "real", or "expected" behaviors from that particular witness.
The way to determine a baseline is asking questions that serve as triggers for reaction. Using the Reid technique, the investigator follows the nine steps to the process and compares the baseline behaviors that the suspect displayed from the beginning of the interrogation all through the final step when the suspect is tired and decides to confess.
The questions are often based on memory. The famous left-eye/right-eye movement theory states that if we draw facts from memory the eyes will move up and to the right; otherwise, if the memory is created on the spot the eye is said to move up and to the left. This is the "Visual Accesing Cue" proposed by Richard Bandler and John Grinder in their book Frogs into Princes: Neuro Linguistic Programming (NLP), and although there is not an intensive body of work on this, there is value to this proposal.
Hence, the investigator should elicit memory such as:
- Where were you?
- Who was with you?
- How long ago have u known the victim?
- Did you and the victim have any arguments?
- At what time....?
- What was the victim wearing?
All these questions, if they can be answered from the suspect's own experience, should elicit all the baseline reactions that the interrogator needs to proceed with the Reid approach.