Thanks for the comment! There’s no hard rule for shuffling - shuffling after each case will result in the most randomness and lower chances of the complete solve for each case, so you can shuffle after each case to increase difficulty.
Alternatively, you can shuffle only after you run out of cards to draw. This signifies the growth of your club’s ability to resolve mysteries through the experience they’ve built up over the many cases they’ve encountered, with a shuffle indicating that a new era of mysteries have come into play that require new ways of thinking.
Let me know which works better for you - I’ll think about incorporating this in another iteration!