He ran towards the Mill Shopping Centre, where some of the early pictures of SoBo leading her normal live were taken, where he abandoned the trolley and made off with the sacks of mail.
Inspector Michaela Kerr who is leading the investigation said:
"Crimes such as this carry many victims - people in the community who will not receive their mail which will result in inconvenience and unnecessary distress.
"This is particularly galling when we know most of the letters will be of no value to the suspect and will end up being discarded.
"I am sure the local community will be keen to support the police in their efforts to identify the culprit and bring him to justice."
Lothian and Borders police are looking for a man about 20-years-old, 5ft 8ins tall and slim. Who was wearing tracksuit bottoms and a black long-sleeved top with white writing when he stole the mail.