Beth, the National Records of Scotland have the following records for him. Not sure if you have seen these. You can order photocopies of papers, on request, from them:
AD14/31/13 - Precognition against Robert Dempster for the crime of murder on the road leading from Craigrothie, Ceres, Fife to Ceres
Dates 1831
Accused Robert Dempster, junior, slater, Address: Cupar, Fife
Victim George MacDonald, Dundee
Also,
JC26/1831/15 - Trial papers relating to Robert Dempster for the crime of murder on the road leading from Craigrothie, Ceres, Fife to Ceres. Tried at High Court, Perth
Dates 12 Apr 1831
Accused Robert Dempster, junior, Verdict: Guilty, Verdict Comments: Guilty in terms of own confession - culpable homicide, Sentence: Transportation - Life
Victim George MacDonald, Dundee
http://catalogue.nrscotland.gov.uk/nrsonlinecatalogue/search.aspxMonica