Latham Letter for pointing out this research report that studied the "guilty look" and concluded that the look is a response to cues from the owner and does not indicate that the dog knows he has done something wrong. Dog trainers and behavior consultants have long known this from their own observations and have tried, often in vain, to convince dog owners that the dog does not know that he has done something wrong, but rather is displaying signs of anxiety in response to cues from the owner. For some poor dogs the cue to display anxious behavior is simply the return of the owners to the home, since a scolding sometimes follows the return of the owner and the dog does not know what to expect.
Horowitz et al. Disambiguating the 'guilty look';: Salient prompts to a familiar dog behaviour. Behavioural Processes, 2009; 81 (3): 447 DOI: 10.1016/j.beproc.2009.03.014
Anthropomorphisms are regularly used by owners in describing their dogs. Of interest is whether attributions of understanding and emotions to dogs are sound, or are unwarranted applications of human psychological terms to non-humans. One attribution commonly made to dogs is that the “guilty look” shows that dogs feel guilt at doing a disallowed action. In the current study, this anthropomorphism is empirically tested. The behaviours of 14 domestic dogs (Canis familiaris) were videotaped over a series of trials and analyzed for elements that correspond to an owner-identified “guilty look.” Trials varied the opportunity for dogs to disobey an owner's command not to eat a desirable treat while the owner was out of the room, and varied the owners’ knowledge of what their dogs did in their absence. The results revealed no difference in behaviours associated with the guilty look. By contrast, more such behaviours were seen in trials when owners scolded their dogs. The effect of scolding was more pronounced when the dogs were obedient, not disobedient. These results indicate that a better description of the so-called guilty look is that it is a response to owner cues, rather than that it shows an appreciation of a misdeed.
Link to more about this article from Science Daily