I found that my players wanted to actually investigate things (not just the initial scene, but other leads too), and that the adventure was woefully unprepared for that to happen.
This is precisely why I recommend y'all to drop the initial scenario - it inevitably makes the players focus on things that the adventure simply is not about (like not even a little; no seriously, the adventure does not write
a single word about the by far most expected development - that the heroes drop everything else and try to find out whodunnit!)
Far better would be to introduce the players as low-level enforcers in the city, making them motivated to carry out the actual scenarios that the adventure is about.
The events of that initial encounter should probably be something the players only hear about in passing. Preferably with comments such as "he had it coming", playing up how the rabble is only suffering under the noblemen's rule, downplaying the "good and just" BS.
The more rpg players hear about a murder mystery, the more they will assume that's the adventure. And that is
completely not the case here.
This adventure should have started with an introduction to local PCs that are motivated to rise in the ranks of the various organiations of the adventure, with
appropriate personalities for the scheming, doublecrossing backstabbing nature of the city.
Having bog-standard do-gooder outsider PCs come to the city and witnessing the initial encounter is the absolutely completely and utterly wrong way to start this adventure. Unless you want it to go off the rails immediately. Unless you force the players to keep to the story, that is. Until they quit in frustration, of course.
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In fact, to be honest I would probably even switch game systems. Everything about this adventure screams Warhammer Fantasy Role-play; where low-life dregs of society is dragged into an apocalyptic conspiracy far above their heads and (probably) against their will.


Also, the expected flow of the adventure, where the heroes are often made to do stuff against their best interests, and where open violence often is the wrong solution is a poor match for "standard D&D" where players are accustomed to doing things their own way. But it is a perfect match for WFRP
I know at least my players would rather kill off any troublesome nobleman than follow his increasingly absurd commands, and that's just wrong for this adventure.
Murderhobo your way through this module, and you completely miss the entire point of it by a mile.