The four are expected to reappear in court in Madrid in the coming days, after a prosecutor presents new evidence.
The trapped Spanish officers had entered the building in Barcelona to detain a dozen Catalan officials and to confiscate documents and materials relating to an independence referendum that Spain had ordered suspended. The contentious vote was held anyway, this past Sunday, and spurred violent clashes between the Spanish police and Catalans.
Hundreds of people were injured, including dozens of officers.
The government in Madrid says the national police had acted proportionally to the provocations, but its representative in Barcelona offered an apology on Friday for the injuries.
Separatist lawmakers have vowed to turn the results of the referendum into a unilateral declaration of independence next week, despite an order from the Constitutional Court to suspend the parliamentary session.
Friday morning, Carles Puigdemont, Catalonia’s separatist leader, asked to appear before lawmakers on Tuesday, a day later than initially scheduled, to circumvent the court’s order.
As the political standoff over Catalonia reaches a boiling point, the loyalty of Spain’s different security forces has become a major point of contention. If Catalan separatists were to declare independence unilaterally, the Spanish prime minister, Mariano Rajoy, would most likely use emergency powers to take full administrative control of Catalonia, which could involve replacing the Mossos with thousands of Spanish police officers.
On Sunday, the national police confiscated ballot boxes after the Mossos declined to close polling stations before the voting, as Madrid had ordered.
The constitutional crisis is forcing companies in the country to adjust their operations, while significantly raising the risk premium demanded by investors for holding Spanish and Catalan debt. Spain’s borrowing costs rose this week to their highest level since March.
On Friday, the board of CaixaBank, the largest financial institution based in Catalonia, was to meet to decide whether to follow the example of Sabadell, another major Catalan bank, which announced on Thursday that it would move its legal headquarters to Alicante.
Relocating would guarantee the banks continued access to funding from the European Central Bank and would allow them to remain under European Union jurisdiction, even if a new Catalan republic were formed outside the bloc and ended up being cut off from the eurozone.
Freixenet, a major producer of Catalonian sparkling wine, cava, also said it would relocate if Catalonia declared unilateral independence.
“People are starting to get scared, and that’s bad news,” José Luis Bonet, the president of Freixenet, said on national radio on Friday. “If we’re really heading for a unilateral declaration of independence, there will be an important departure of companies from Catalonia, which would cause very serious damage.”
This week, Mr. Puigdemont, Catalonia’s leader, requested international mediation to help resolve the conflict, but the proposal was rejected by the prime minister and fell on deaf ears in Brussels and other capitals in the European Union.
But the Foreign Ministry of Switzerland, which is not part of the European Union, is offering to mediate the conflict, according to Swiss national radio.