First of all, sorry for including Spanish quotes, but I just wanted to include a few things from the Spanish press...
First, it is true that there was a rewiew of the incident, but what was being asked was for an independent investigation too (common in Spain when the military is concerned). In these terms, Judge Pedraz had asked for documentation and statements from the military men involved:
"Pedraz recuerda que ha cursado dos peticiones de auxilio judicial a los Estados Unidos, una el 21 de abril de 2004 solicitando documentación y la otra el pasado 6 de junio pidiendo que se tomara declaración a los militares imputados 'o bien que se autorizara el desplazamiento de una comisión judicial española hasta territorio estadounidense para la ejecución de esas declaraciones'." From EFE.
These request did not received any answer, not even a rejection. That is why the warrant was issued as the last resource...
In any case, the public prosecutor ("fiscal") is going to asked for the revocation of the order (I am not sure of the name in English, in Spanish would be "recurrir"), since assumed that the legal terms are not satisfied:
"La Fiscalía de la Audiencia Nacional recurrirá mañana el auto alegando falta de jurisdicción, falta de competencia y falta de "título extradicional".
Fuentes del ministerio público consultadas por EFE explicaron que el juez carece de competencia para investigar la muerte de un ciudadano español "producida en el ámbito de un conflicto bélico" y añadieron que no existe ningún delito de persecución internacional sobre el que sustentar la orden de detención." From EFE.
That is, the order is most probably null from the international agreements. Not only the soldiers cannot be extradited if in the US, but even if they travel to other countries in a militar contingence. The question was open about if they could be arrested in other countries if traveling as civilians... But again, according to the agreements, it should not happen...
Note: I do not agree with the terms of the resolution from Judge Pedraz, but I always support an independent investigation in these situations. And if the situation involved nationals from other countries, collaboration with them should always be provided, or at least, not ignored...