Defendants may find themselves taken into custody if they travel abroad. Their assets could be seized in other countries.
“It starts a process of accountability,” said Stephen J. Rapp, former United States ambassador at large for the Office of Global Criminal Justice and now a nonresident fellow at The Hague Institute for Global Justice, who helped to file the case. “We could have international arrest warrants in a month or two against these individuals.”
The defendants include Vice President Farouk al-Sharaa, a former foreign minister; Ali Mamlouk, head of the National Security Bureau; Gen. Jamil Hassan, head of air force intelligence, one of Mr. Assad’s most feared organizations; and senior officers running the prison where Abdul was detained and killed.
The case “will specifically allow the courts to investigate the torture and execution of thousands of civilians in the illegal detention centers” operated by Mr. Assad’s government, according to lawyers in London and Madrid with the Guernica 37 International Justice Chambers, a legal advocacy group that represents Abdul’s sister.
“Very few defenses apply” to the charge of state terrorism, said Almudena Bernabeu, a partner in Guernica 37 who has prosecuted senior El Salvadoran officers and other officials implicated in crimes. “There is a big presumption of guilt.”
The case reflects accelerating efforts in Europe to bypass the political obstacles that have thwarted access to other international justice remedies for crimes committed in Syria’s war.
Russia, a key ally of Mr. Assad, has made clear that it will use its veto power at the United Nations Security Council to block Syria’s referral to the International Criminal Court. China has vowed to follow suit.
European prosecutors have started more than 20 cases against individuals for war crimes, but all have focused on low-ranking perpetrators from opposition armed groups or jihadist forces. The case in Spain targets the Syrian government and high-ranking officials.
Judge Eloy Velasco ruled that Spain’s national court had jurisdiction to hear the case because the plaintiff is a Spanish citizen, and that under international law, relatives of people who have disappeared or died from crimes committed elsewhere are also victims.
Ms. Bernabeu called the judge’s ruling “a landmark decision not only for the victims’ fight for justice but also for the requirements to investigate and prosecute international crimes in national courts when other international institutions such as the International Criminal Court have proven unable to do so.”
Germany’s federal prosecutor has agreed to hear witness testimony in a case filed in March by the Berlin-based European Center for Constitutional and Human Rights and two Syrian lawyers, Anwar al-Bunni and Mazen Darwish, which accuses six high-ranking Syrian officials with war crimes and crimes against humanity. The center has not publicly identified the officials, and it is unclear when, or if, that case will advance to a court.
Guernica 37 lawyers are also preparing a case relating to the death of Abbas Khan, a 32-year-old British doctor who had traveled to Syria to treat war casualties and died in a Damascus prison in December 2013. Syrian officials said he had hanged himself in his cell days before the government had promised to release him.
The case undertaken in Spain began when a WhatsApp message appeared on Amal’s phone during her lunch break showing a photo of Abdul’s face taken after his death, Ms. Bernabeu said.
Abdul’s photo was among the 55,000 images brought out of Syria in 2014 by a former police photographer known by the pseudonym Caesar, documenting the deaths of more than 6,700 individuals in Mr. Assad’s prisons.
The Syrian Association for Missing and Conscience Detainees, an activist group, posted about 3,000 of the Caesar photographs on Facebook in March 2015. Abdul’s son, who has escaped to Turkey, spotted what he believed was his father’s face and sent it to his aunt in Madrid.
Confirming that Abdul was the man in the photograph was not easy, Ms. Bernabeu said. His face and body were emaciated, with burn marks. His limbs appeared to have been broken.
Abdul’s identity was confirmed by his widow during an emotional Skype call in which Ms. Bernabeu showed her the Caesar images, and she identified surgery scars.
Syrian activists have welcomed the Spain case but remain frustrated that Mr. Assad and his subordinates have yet to answer to an international tribunal.
“The realistic chance of arresting any of them and bringing them to trial is very slim,” said Mohammad al-Abdallah, a former detainee who is now executive director of the Syria Justice and Accountability Center in The Hague.
Others still saw progress.
The Spain case is “not a panacea by any means, but in a conflict that has been without any positive symbols, this is potentially positive,” said Cameron Hudson, director of the Simon-Skjodt Center for the Prevention of Genocide in Washington.
He said the case could show that “there is an end that we can get to that would involve some measure of justice and accountability.”