Mutual Legal Assistance and Extradition
His Majesty's Procureur (H.M. Attorney General) is the central authority in the Bailiwick of Guernsey (which comprises the islands of Guernsey, Alderney and Sark) for the purposes of providing mutual legal assistance and dealing with extradition requests.
Mutual Legal Assistance
A guide on making mutual legal assistance requests is available here - 
Mutual Legal Assistance Guidance [465kb]
Extradition
A guide on making extradition requests is available here - Extradition [280kb]
Contact details
His Majesty's Procureur
St James Chambers
St Peter Port
Guernsey
GY1 2PA
Telephone: +44 (0)1481 221600
Email: GuernseyILOR@gov.gg
Website: www.guernseylawofficers.gg