Chapter I General Provisions
Article 2 (Restrictions on Assistance)
Assistance shall not be provided in any of the following circumstances:
(i) When the offense for which assistance is requested is a political offense, or
when the request for assistance is deemed to have been made with a view to investigating a political offense;
(ii) Unless otherwise provided by a treaty, when the act constituting the offense for which assistance is requested would not constitute a crime under laws and regulations of Japan were it to be committed in Japan;
(iii) With respect to a request for examination of a witness or provision of articles of evidence, unless otherwise provided by a treaty, when the requesting country does not clearly demonstrate in writing that the evidence is essential to the investigation.
EDIT.