It matters more than Locus thinks, which is why Wash is pursuing it. Every answer tells him a little more of what he needs to know to come to a conclusion on Locus. The best thing to do now is stay on the level and keep him talking.

On one hand, given that the Reds and Blues are still alive last time Wash checked, he can't say he's surprised at Locus' answer. On the other hand, for someone who doesn't like to make their own decisions in the interests of avoiding Consequences, that's one hell of a decision to make.

So he nods - understood - and continues. "Did you kill him yourself, or did you let them do it?" So he'd made a decision; just how active was he in its execution?