I have told my Fact Investigation students that planning for a witness interview is often somewhat like planning for trial.
This leaves the question: What does planning for trial involve?
The answer: Many things.
But some of the things one must usually plan for are shown below:
In this trial plan the trial lawyer has struggled mightily to order the calling of the witnesses so that together they tell a story that begins at the beginning, moves to the middle, and ends at the end. As you can see, the lawyer has largely but not entirely succeeded. Such is life -- and such are the vagaries of the evidence that witnesses have in their heads and of the legal rules that govern the calling and re-calling of witness.
Now an interview is not an exact replica of a trial. Indeed, there are many differences between trials and pretrial interviews of witnesses. But the requirements of possible trials sometimes do and should cast a backward shadow on pretrial interviews. (Of course, one might wonder how a thing that does not yet exist and may never exist can cast a shadow on an earlier event. But that is a metaphysical question that I leave for another day.) So one might well decide -- and rationally and sensibly so -- that a pretrial interview should be designed in part to ferret out, if possible, evidence that would or might satisfy the requirements for victory at trial. One possible witness interview plan, thus, might look like this:
A different witness interview plan might look like this:
Of course, neither of the above interview plans is comprehensive. An interviewer might have and almost certainly will have interview objectives in addition to those sketched above. For example, a central objective might be to establish rapport with the witness. Another objective -- sometimes a key objective -- might be to explore the credibility or bias of the interviewee. Yet another objective might be to see if the witness' testimony presents certain themes that may arise during the testimony of other witnesses. And so on. But the multiplicity of the interviewer's objectives should not lead the interviewer to abandon all planning. To to do so is usually fatal.
The dynamic evidence page
It's here: the law of evidence on Spindle Law. See also this post and this post.