A woman reacts as she looks at a gruesome collection of images of dead bodies taken by a photographer, who has been identified by the code name “Caesar.” The photos were displayed at the United Nations headquarters in New York in 2015. A Spanish citizen who identified her brother in the collection is bringing a case against nine Syrian officials. (Lucas Jackson/Reuters)

The first criminal case in a Western court against members of Syrian President Bashar al-Assad’s government began with a WhatsApp message.

Amal was alone in her hairdresser shop in a working-class neighborhood of Madrid when she clicked on the link. The face of her long-lost brother, Abdul, popped up on her smartphone.

Amal and her younger brother, Abdul, were inseparable growing up in an upper-class home in a village in Idlib province in northwestern Syria. Amal left Syria at the age of 19, following her fiance, a medical student, to Spain and later she became a Spanish citizen.

Before the outbreak of the Syrian civil war in 2011, Amal would fly home to visit Abdul and her family at least once a year. They kept in touch on WhatsApp, and spoke on the phone about once every 10 days — until a January afternoon in 2013 when Abdul, at age 43, disappeared.

Amal was not sure what had happened to her brother — until that moment in 2015 when she stared down at Abdul’s lifeless, dirt-covered face, half in shadow. There was a piece of white tape on his forehead with illegible markings on it. The picture had been found on the Facebook page of a human rights group and forwarded to Amal by a relative.

Once Amal had recovered from the shock of seeing her dead brother, she sent a message to the Facebook page in which she provided Abdul’s full name, along with her contact information. She included a photo of Abdul from before his arrest by Syrian forces.

Amal did not realize it at the time, but her response had opened a legal pathway which international war crimes investigators had long been waiting for.

As a Spanish national, Amal could bring a case on her brother’s behalf.

In a complaint filed on Wednesday with the Spanish National Court in Madrid, she was identified as the “indirect victim” of the crimes which were allegedly committed against her brother.

The 95-page complaint singled out nine Syrian individuals as those responsible for Abdul’s death. They ranged from senior officers at the intelligence branch, where he was tortured and killed in 2013, to the leaders of the Syrian intelligence and security services who oversaw his detention and thousands of others.

The complaint accuses the nine defendants of state-sponsored terrorism. Stephen Rapp, who led the State Department’s Office of Global Criminal Justice until August 2015, said the grounds were similar to those brought in Cold War-era cases against Latin American leaders.

The complaint was filed by a legal team led by Almudena Bernabeu, a San Francisco-based lawyer who brought a similar case in Madrid in November 2008 that resulted in a Spanish court order for the extradition of El Salvador’s former vice defense minister for alleged war crimes.

Many of the details about the criminal complaint have not been made public, including the full names of the victim and his sister, to protect their family members still in Syria. Spanish prosecutors asked Amal’s legal team not to disclose the names of the nine defendants, in hope that they could be caught unawares outside of Syria and apprehended.

Country code 34

The Spanish case emerged from a grim trove of more than 50,000 postmortem photographs which were taken at Syrian military hospitals between 2011 and mid-2013 and then smuggled out of Syria by a military-police photographer later code-named Caesar. From the 50,000 photos, 6,700 individual corpses were identified.

Activists working with Caesar started to post many of the images on a Facebook page in March 2015, in hopes that family members in Syria and around the world would come forward to provide information about their loved ones. The goal was to identify the victims and create a database that could be used to bring war crimes charges against members of the Assad government.

The photos posted on the Facebook page were cropped to show just faces and exclude gruesome details about how the victims were tortured and starved.

Soon after the photos were posted on Facebook, Abdul’s eldest son spotted his father’s face on the website. He showed the image to his mother, who was not convinced that it was him. Abdul’s family in Syria sent the picture to a niece in Egypt, who, in turn, sent the link to Amal.

The three-seat hairdresser shop, located in the Chapinero neighborhood, was empty when Amal saw the image. It was lunchtime, and she had no customers. She said her body started to shake.

The Facebook page was managed by a group called the Syrian Association for Missing and Conscience Detainees, which had an office in Istanbul and took the lead in analyzing the Caesar photos. The FBI had reviewed the trove and concluded that they were authentic.

On April 28, Rapp visited the group’s Istanbul office and was given a printout listing the names, phone numbers and email addresses of victims’ families willing to cooperate in any future legal proceedings.

One of the numbers on the list jumped out at Rapp. It started with the country code “34” — the one for Spain. Eureka, Rapp said he thought. The printout also listed a “hotmail.es” email address for Amal.

Rapp knew that Spanish prosecutors had a tradition of going after high-level international actors.

Spanish law would allow the first prosecution targeting members of the Assad regime in the West — but only if the family member in question was a Spanish national.

“Exciting possibility in Spain,” Rapp wrote on May 5 to Bernabeu and Zakariya Sallan, of the Syrian Association for Missing and Conscience Detainees.

On May 6, Sallan wrote to Rapp and Bernabeu after talking to Amal by phone.

“She has important information,” Sallan told them. Not only was she a Spanish national, he said, but “she is the victim’s sister and ready to work with [Bernabeu].”

“This is great news!” Rapp said in response.

Bernabeu met with Amal at her hairdresser shop in July.

Amal asked to see a full-body photograph of her brother’s corpse.

Bernabeu pulled out her laptop and brought up one of the photos. It showed Abdul’s emaciated body strewn on a dirt floor. His hands were clenched and covered in dust. He wore brown-colored underwear and nothing else. Burn marks were visible on his neck and body. Markings on and next to his body identified him as a detainee and indicated which intelligence branch was holding him.

Amal told Bernabeu that her brother was the one who everybody in her large family admired the most. He dropped out of school at the end of the ninth grade. He went from driving a bus to having his own taxi. Later, he got a van and became a delivery driver. He drove a 60-mile daily route resupplying small shops that sold sodas, snacks and other supplies. Investigators think government forces may have thought he was providing supplies to besieged areas. Amal said he was not politically active. “Nobody understands how and why he was picked up,” she said in an interview.

Amal provided Bernabeu’s legal team with pictures of Abdul from before his abduction. One showed him wearing a loosefitting, short-sleeve, V-neck shirt and sitting on his living-room couch. He looked healthy and happy.

The “before” shot was labeled as exhibit #9 and submitted to the Spanish National Court on Wednesday along with 3,600 pages of evidence.