Framework Decision 2009/948/JHA on prevention and settlement of conflicts of exercise of jurisdiction in criminal proceedings (30th November 2009) (“CJ Framework Decision”) defines parallel proceedings as “criminal proceedings, including both the pre-trial and the trial phases, which are conducted in two or more Member States concerning the same facts involving the same person.”
It is not unusual during EAW proceedings for your client to be faced with parallel proceedings in two or more EU Member States for the same facts, i.e. that there is a conflict of jurisdiction. The conflict may arise between the Executing and Issuing Member States, or between the Issuing State and a third EU Member State, which might involve competing EAWs (Article 16 EAW).
EU law has a very underdeveloped legal framework on this topic. The CJ Framework Decision only establishes information sharing and consultation obligations between the Member States, as opposed to binding criteria or procedures through which the jurisdiction of prosecution must be decided.
It should be noted that conflicts of jurisdiction are an issue dealt with between prosecuting authorities where the defence may not have had an opportunity to intervene. Therefore, the EU legal arguments suggested below might not have been tested and there is no EU case law to provide guidance on the topic.
Ultimately it should always be kept in mind that solving conflicts of jurisdiction in parallel proceedings against the same person for the same facts aims primarily at preventing the violation of the ne bis in idem principle, which is a fundamental right laid down in Article 50 CFR (see section E.1).
 Conflicts with third states will not be addressed here and are in principle a matter for national law.