Artikel 20

A person who is a national of or habitually resident in a Contracting State and who is summoned by name by a court or tribunal in another Contracting State, or by a party with the leave of the court or tribunal, in order to appear as a witness or expert in proceedings in that State shall not be liable to prosecution or detention, or subjected to any other restriction on his personal liberty, in the territory of that State in respect of any act or conviction occurring before his arrival in that State.
The immunity provided for in the preceding paragraph shall commence seven days before the date fixed for the hearing of the witness or expert and shall cease when the witness or expert having had, for a period of seven consecutive days from the date when he was informed by the judicial authorities that his presence is no longer required, an opportunity of leaving has nevertheless remained in the territory, or having left it, has returned voluntarily.