Sounds like maybe the solvable problem that stood out to your players was not "whourdered your friend?" but instead "Why are the guards being so obtuse?" and thus they took the lead on that hook, rather than the one you intended.
Perhaps it's an issue of presentation. As players, I think we are often looking for the immediately actionable information, and as GMs we often forget that the players aren't privy to the way our brain works, or the details about the scenario that know. We therefore put information in obtuse terms, thinking its obvious to intuit. And we don't always think about how important or immediate some things that we consider incidental might appear to our players.
I always try to make sure that players have useful, actionable information out of a scene where possible. And I am not afraid to address the player to clarify their character's understanding.
Oooor perhaps you got a problem group, or you rubbed em up the wrong way somehow, sparking some rebellious passive aggressiveness.