Somehow, my players are not convinced that Sephek is the killer. After Hlin stated her case, my players headed to Bremen since that where Hlin thinks Torrgas will be next. I let them relax there for a day before having Torgs show up. After browsing her wares, and eyeing up Sephek, they decide to retire to the Inn (Buried Treasures) which is the same place Sephek and the rest of Torgs were staying as well. I had him sit alone in the corner, and then walk around outside in the dark so the players had ample opportunity to confront him, buy to no avail. A player who is playing as a fairy even slipped under his door to spy on him, and he was staring at a wall the whole night.

It's the next day now, and my players still don't want to confront him about it, since they don't have hard proof.

Any advice?