Constitutional law professor Javier Pérez Royo believes that the imprisonment of Oriol Junqueras, Jordi Sànchez, Jordi Turull, Josep Rull and Raül Romeva has technically been illegal since 28th April.
The professor, in an article published by eldiario.es (link in Spanish), argues that from the moment they were elected to Spain's Congress or Senate that day, they should have been free. He argues they enjoy the right to parliamentary immunity and cannot be charged or put on trial without the parliament's permission, called suplicatorio in Spanish.
Pérez Royo states that the Supreme Court should send suplicatorio applications to the Congress and Senate. Once approved, they could then continue with the trial "in the matter the believe appropriate".
He says that if the court rejects the petition from defence counsel seeking the suplicatorio, they should appeal to the Constitutional Court, which should in turn suspend the trial provisionally whilst they consider the appeal. If the appeal, a type called amparo in Spanish, is turned down, they could then turn to the European Court of Human Rights to request the suspension of hearings.
The professor says that not only does the Supreme Court have to confront the fact that five of its prisoners have been elected to public office, but also the more than likely election of Carles Puigdemont and Oriol Junqueras as MEPs later this month. He says they won't be able to stop Puigdemont taking his seat and predicts a new legal battle in Europe.