Didn't Legion say that most people would think of it as a machine and easily disposable? That could be a reason they wanted to do it, just to see if changing its programming could work.

Otherwise, we don't know that the rest of the VIPs aren't killers already. We've already got one admitted killer here, why wouldn't we have more? Isn't the whole part of avoiding suspicion is to blend in with the rest of the crowd?