You can't have an emergent mystery in terms of who is truly guilty.
You can, however, have an emergent mystery in terms of what the consequences end up being.
Because I did exactly that. I had a murder mystery, with only a little bit of magic involved. There was a clear, singular perpetrator the entire time and I knew who they were.
But there were several suspects, and multiple layers of political wrangling, and the possibility of at least three distinct diplomatic incidents as a result of this murder if the wrong people were accused, and further possible blowback against the party's sponsoring city-state (whose Sultana had made them temporarily diplomatic representatives for her government.) That's where the emergent properties come into play. We already know the danger, there's no question that the ultimate problem is "do we find the killer or not?" But what created tension and allowed for the players' individual actions to shine through, just as a "do we stop the bad guy or not?" story would, is that there were many ways things could cash out, some of them great, some of them terrible, many in-between. Ultimately, the party succeeded with flying colors and even ensured that the political machinations which got them into this in the first place ended up going very smoothly and having nothing but positive impacts on their royal sponsor. Had they missed too many clues or misinterpreted those clues, however, they could have enabled the real culprit to trigger a state of war (or at least armed conflict) between two or three Jinnistani city-states, weakened their sponsor's diplomatic position, and empowered one of their rivals to reap massive financial windfall from supporting both/all sides of the resulting conflict.
The irony, of course, is that the critical clue which ensured the downfall of the real killer was that the servants knew she had received a red dress by post before the party, but was seen actually attending that party in a blue dress. An excellent coverup blown by someone being overly finicky with their fashion choices.