Tina Obrien said in an interview that Sarah will have frequent visions and flashbacks of Cllum, she is also watched by someone at his funeral and Bethany receives gifts from a "secret admirer". Gemma did tell David to watch his back, so maybe Callums mate are the ones behind it but I think it would be a good twist if it turned put to be Callum himself. I have a feeling that the police will eventually question Denton to then find out that he is also missing. So the police might assume that he has ran away because he was the one who done it. When really its his body that has been misidentified as Callum.

Yeah its a pretty rubbish theory but I would prefer this to happen than someone simply getting arrested for it and then thats that.