[B is fully aware that his laugh scares Mello; it scares everyone. But that doesn't stop him from laughing. It is a good scare-tactic, sometimes. To stop Mello from struggling he twists his arm just a tiny bit further, only for a second, to send threads of sharp pain through the limb. Like the threatening brandish of a whip.]

That does not answer my question. Was he working on the case, or was he not?