As you run past the child, you loose the scent, backtracking you find it once more, and again you loose it. With agonizing slowness you retrace the scent, exploring it through the area. He came through a third of the four alleyways, he engaged the guards, he stabbed the merchant, and then... there It vanished at the merchant, or more precisely it vanished into the blood pooling at his feat, where his scent blended then became the overwhelming smell of iron in the blood.
OOC
Spoiler
By no means, that's just a side bonus, the initial hook is indeed the true hook.
Surely I couldn't have expected someone who only had the spiffy fighting style to be an adequate obstacle to make this challenging for a trained assassin now, do you?
OOCly, note that to each of you the assassin looked like he went through the alleyway that each other came from. Surely that doesn't mean the assassin actually did.