In that lower hallway, Dufgal and the others see that the dried bloodstains the thief called out earlier are not just present, but plentiful. And in that blood there are tracks -- bootprints, leading to the steps they just descended. But by the time they reach the bottom of the stairs, the blood has thinned and the prints disappeared.
A quick peer into the doorway at the end of that narrow passageway reveals that it is the space below the bowl-like depression in the upper chamber, one of the first rooms the adventurers encountered. It is in fact the bottom of that pit-trap, and fully a score bronze spears are set into the ground, awaiting anyone falling from that chamber above. A circular hole is visible in the ceiling, big enough for two people to fall through at the same time... surely leading to that upper room.
Beneath the hammered spears, on the floor of this lower chamber is a lot of dried blood. More than a single body might contain. And in that nasty mess, a pair of daggers glint, resting in the middle of that forest of spears.