Brave Derrin's "B" killer? (spoiler)

[Falco]

Does anyone know where I can find this "B" guy that owns the dagger I found in Derrin's body? I looked everywhere in the Gift and found nothing. I know I can finish the quest talking to his mother, but I would rather find his assassin first.
Any help?

[Crusader King]

Top left of map there's a group of thugs and one of them is a named npc.

[Falco]

Ty

[Crusader King]

No worries.