You think quickly. You can smell smoke coming from a nearby room; you assume that that's where the guards would be heading. "I can take care of this," you say, waving away the guards. Picking up the Stormwind officer's body, slowly enough that you could be stopped if you stepped out of line, you approach the room, gaining no resistance from Vanessa or the other Defias members in the process. The room you enter looks to be an abandoned goblin foundry...abandoned, that is, except for the few Defias workers scattered around the titanic facility. Looks like your suspicions were right; this is, in fact, a place where someone could be conveniently "disposed" of. While you take a look around, the officer wakes up. You can't tell if he doesn't recognize who you are, if he doesn't realize that you're trying to save his skin, or if the concussion you just gave him knocked all sense out of his head. He starts trying to speak.
He's about to compromise your position. Do what the guards would have done before your whole purpose in here is given away. Explain to him what's going on. Maybe that'll get him to not give you away. Muffle him, take him to a separate room, then explain things to him, and hope he doesn't give you away during the process.