Prolix,
Hopefully that quest has already been adjusted so that the evidence is lost, compromised or deemed not enough. We do try to make sure there are no quests that would result in the final removal of an NPC from the world, such as by true death or long-term incarceration. That would indeed break the realism a bit (Hi NPC X, didn't I just send you to jail yesterday?) , so if you can think of the name, tell me and I'll check it out.