Wow.. Can you please give the link to the post? I would like to see if there's a hint how they did it..
As for now, I assume they use one set for suspects and the other set for question card. In that case the question might be really straight forward, like 'do you have ace of base?', and the answer will be either 'yes' or 'no'.
... or probably we can ask with more then one question card? like 3 cards at the same time?
Thinking it over now, I think they did mean to just write over the cards with a sharpie or so -_- I guess that makes some sense...