Letters Rogatary is a formal request process between courts in different countries and is a way to request important computer forensic evidence which may reside within the jurisdiction of foreign countries. This process is extremely slow and is often used as a last resort. The U.S. Department of State has specific advice for the Preparation Of Letters Rogatory.
In the United States of America, we have established treaties (called Mutual Legal Assistance treaties) with many countries to formalize this information sharing process and increase the overall success of the exchange.
