If the conflict is not resolved, both (or more) Member States will proceed with their cases and the decision that first becomes final will prevail, pursuant to Article 54 CISA and Article 50 CFR.
Should this happen, your role, together with the ISL and if applicable the third EU Member State lawyer, is to seek a final decision to be reached first in the Member State that you consider to be the most appropriate for your client to be prosecuted.
If coercive measures are ordered in both (or more) parallel proceedings, you should consider invoking EU law and using a transnational rights approach to challenging them, for example:
According to EU law the person may only be tried once for the same facts (Article 50 CFR and Article 54 CISA). It follows from this that the person may only serve one sentence. Any detention periods served for the same facts should be accounted for in that sentence (Article 50 CFR and Article 56 CISA).
Consequently, even where there is a risk of absconding, or interfering with witnesses that might usually justify remanding the person in pre-trial detention, you could argue that it would be disproportionate pursuant to Article 6 CFR/ 5 ECHR to impose subsequent pre-trial detention periods in two or more Member States that, notwithstanding respecting national laws, are disproportionate taking into account that only one sentence for the same facts may be imposed and enforced in only one of the Member States (for example, if the person is being prosecuted in different Member States for the same facts that carry a sentence of up to one year of imprisonment and has already spent six months in prison in one Member State and six months in another Member State, it would be disproportionate to remand her in pre-trial detention, irrespective of the risk of absconding, since she has already been detained for the time equivalent to the maximum sentence that may be imposed).
Freezing of Assets
If there are cumulative orders freezing the assets of the person in parallel proceedings, they may be challenged on grounds of proportionality (Articles 17, 50 and 52 CFR).