There's a person in the way. Maybe it's an Intrepid Reporter, or one of those Meddling Kids. It would be convenient if this inconvenient individual could be removed from the picture... permanently. But a murder rap would really make things even more inconvenient, especially if you're a Villain with Good Publicity who really cannot afford bad publicity. So your primary option as a Big Bad is to hire someone to take care of this little problem. But it can't look like murder, and it can't just be a mysterious death. Examples of Make It Look Like an Accident include: