Article 7 of the European Convention on Human Rights sets limits on criminalisation, forbidding ex post facto criminalisation by signatory countries.
Case of the Parot doctrine.[1]
Book: Law of the European Convention on Human Rights . 2nd . Harris . David . O'Boyle . Michael . Warbrick . Colin . 2009 . Oxford University Press . New York . 978-0-406-90594-9 . 331–339 .