That's Odd

You drop down the manhole and head north. (I sent you a paintbrush map.) To the south is where you battled Fast Eddie, to the north should be the main east-west pipe that had the rigged catwalk and the first couple of bodies that you found.

(The caltrops are still to the south but scattered, you can waste time picking them up and trying to to get pricked by the poison if you want, I wouldn't bother.)

Now that Kaspar is conscious, he can see the distance from the manhole opening to the main east-west pipe quite easily with his darkvision (what's Castille using?). It is roughly 45 feet from where you drop down into the sewers to where this pipe empties out to the main east-west pipe.

Kaspar can easily see footprints...kobold footprints. Left in the muck from when he was looting the bodies. You don't have any ranks in Survival or Knowledge Dungeoneering, but you are reasonably confident that the prints are that of the kobold that you slew.

But...where are Fast Eddie's footprints?

He fled north, and he didn't go up the manhole to the street or else he would have been arrested...