Should consultation proceedings commence, as set out above, EU law does not explicitly give you a right to intervene. You should ascertain whether your national law gives this right, i.e. to be informed of the positions of both Member States, to make representations, be present in any meetings between the authorities, and to be informed of any decisions.
Since there is no guarantee that you will be able to intervene, your application for consultation proceedings to be launched should include detailed representations on the defence perspective as to the most appropriate jurisdiction.
Can you challenge a decision on jurisdiction? At the moment the decision on waiving or maintaining jurisdiction is a matter of national law and you will only be able to challenge it in accordance with procedures established under national law.
If you have not had the chance to be heard or to intervene in consultation proceedings, you could try to challenge the decision of your national authority invoking Articles 47(1) and (2) CFR in conjunction with the CJ Framework Decision (the Charter only applies where there is relevant EU law in scope).
Article 47(2) provides that “Everyone is entitled to a fair and public hearing within a reasonable time by an independent and impartial tribunal previously established by law”. Since the CJ Framework Decision was enacted to prevent the infringement of the ne bis in idem principle, already protected by Article 54 CISA and Article 50 CFR, which is a fundamental right of the person concerned (see Recital 3), it could be argued that the suspected or accused person should be entitled to be heard on this matter. The provisions in the CJ Framework Decision concerning consultation proceedings should therefore be interpreted in conformity with Article 47(2) CFR. A reason not to allow defence engagement could be the “protection of the investigation.” Usually when there are EAW proceedings involved, this justification should not be invoked as a reason to restrict the intervention of the defence in this process, since the person will already be aware that there are multiple investigations taking place. Where there might be compelling reasons not to involve the person due to the need for “protection of the investigation”, they must have the right to challenge the decision on the best placed jurisdiction to prosecute as soon as those grounds cease to exist and at the latest when a formal indictment against him/her has been brought.
Article 47(1) provides the right to an effective remedy. This could be invoked as a legal basis for challenging a decision on jurisdiction, in particular where the defence has not been able to exercise the right to intervene and convey its views, contrary to Article 47(2).
When requesting or challenging a decision on the choice of jurisdiction, you might also want to consider invoking procedural Charter rights (for example, if legal aid is manifestly insufficient or lacking in quality in a given Member State you could try to argue that choosing such a jurisdiction would constitute a violation of Article 47(3): “Legal aid shall be made available to those who lack sufficient resources in so far as such aid is necessary to ensure effective access to justice”).
These provisions could also be invoked in order to seek to intervene in any consultation procedures under the auspices of Eurojust. It will be necessary to overcome the rule of confidentiality (Article 25 Eurojust Decision), which the arguments suggested above could be utilised for, among others. If nothing more, it is possible to at least request access to personal data stored at Eurojust, notwithstanding certain limitations, and to appeal to Eurojust’s Joint Supervisory Board if no information is given (see Article 19ff Eurojust Decision). This route could be used to determine what decision has been made about jurisdiction.