Re: interviewing a witness
Most people would understand an "interview" to include the whole face-to-face meeting between the lawyer and the witness. Questioning would be a specific - and very important - part of the interview, but not all of it. The lawyer would also be gaining impressions of the witness through observing her physical reactions.
The difference between interrogating and questioning is not necessarily the depth and detail involved, but the fact that an interrogation usually has elements of formality and duress involved. A guest celebrity may be questioned - even in great detail - on a TV show, but a prisoner in a police "interview room" will be interrogated.
Oops, SoothingDave; didn't see you get in first.
I'm not a teacher of English, but I have spoken it for (almost) all of my life....