They have not interrogated me as such, just asked me the same questions in a very polite manner. I asked about whether I should contact a lawyer and they gave me some telephone numbers/advice etc. but said it was just routine questioning.
With regards to other comments - not the husband as he was in China(?) with work. My wife was also away at the same time otherwise I would have an easy alibi. And I count going out for lunch during the working week as still being "inside work". We never met/spoke outside 8-18.
I am increasingly worried for her as she had her fair share of Facebook 'admirers' - to the extent that she abandoned social media last year.
Hey ho, I'll update if things progress.