A detective is called to investigate a reported home burglary. The homeowner — who lives alone — says she returned from a three-day work trip to find her house ransacked. The detective observes four things: (1) the rear sliding door is shattered, the frame pried from outside; (2) the bedroom has been turned over, jewellery and cash are gone; (3) a half-full cup of coffee sits on the kitchen counter, still faintly warm; (4) the homeowner's German Shepherd — described by neighbours as aggressive toward strangers — is lying calmly in its dog bed, water bowl freshly filled. The detective suspects the homeowner staged the burglary. Which single observation most directly supports that conclusion, and why?