The rockets sounded different that night. This time they lacked the explosive impact that had so frequently accompanied attacks on opposition-held areas in Syria.

On August 21, 2013, rockets loaded with sarin warheads were launched into eastern Ghouta. Cooler weather allowed the nerve gas to permeate into lower levels of buildings as it spread across parts of the rebel stronghold.

"It was like Judgment Day, as if people were ants killed with bug spray," says Eman F., a trained nurse and mother of three children. "Many people were dead on the road, cars stopped, people packed into them [as if they died trying to flee]."

Eman told her brother to take the children to safety before she rushed to the local hospital where she worked. Her husband Mohammed followed shortly after to assist with first aid.

Throughout the conflict, civilians have often sought shelter from airstrikes, shelling and other indiscriminate attacks in the lower levels of buildings, and this particular night would be no different.

"Many people came to the hospital because the hospital is in a basement," says Mohammed. "I went to my wife and told her to come outside and see what was happening. When I went back up ... a rocket landed in front of the hospital. I couldn't feel anything."

Eman weeps as she recalls resurfacing from the basement to see what was unfolding, only to find her husband convulsing on the ground like dozens of others around him.

"It was a terrible scene that I cannot describe to you," Eman tells DW, as the cigarette she holds starts to burn through the filter. "I did not know what had happened. I left to get atropine injections to help my husband in case of suffocation."

"When I returned to give him the needle, my colleague and I didn't feel anything nor do I remember anything after."

Sarin, a chemical warfare agent, had gripped its victims. Its odorless presence only made itself known after it had already begun to paralyze the body's respiratory system. In most cases, those who did not survive died of asphyxia.

Survivors blamed the Syrian regime for the attack.

Miscarriage of justice

Eman still struggles with what she saw that August night in eastern Ghouta. The panic attacks are a constant reminder of what she lost — including her eldest child.

The parents discovered the fate of their 19-year-old son when a relative identified the boy days later in images posted online. They were never given the chance to recover his body, which was buried in a mass grave shortly after the attack.

But they aren't the only ones who lost a loved one that night.

At least 1,000 people were killed in the attack, including more than 400 children, according to several independent sources.

Targeting civilians with the use of chemical weapons constitutes a war crime under international law.

"To this day, I imagine the children who were dying in front of my eyes," says Thaer H., a Syrian journalist who documented the attack. "I was not a medic. I did not know how to save someone dying in front of me — we were not trained on how to deal with [toxic] gases."

At the time, Thaer worked for the Violations Documentation Center, which sought to record human rights abuses during the Syrian conflict. He shared with DW the harrowing footage he captured that night.

The images show bodies writhing on the ground, some foaming at the mouth, while others scream for help. Victims appear to swallow in a last bid to bring air into their lungs after their respiratory systems had effectively stopped functioning.

Thaer's colleague Razan Zaitouneh, who founded the center and assisted him in documenting the attack, was kidnapped shortly after and never heard from again. Thaer eventually managed to flee Syria for Germany, where he now resides.

"I got scared at first and I grabbed the camera," says Thaer. "But I turned it off after I saw children die in front of me. Then I thought: If I don't film, who would report on what had happened to these people?"

Between war and the courtroom

The brutal attack shocked much of the world and nearly triggered military interventions from France, the UK and the US. When plans for Western operations against the Syrian regime collapsed, international efforts turned toward the International Criminal Court (ICC).

However, Russia and China, veto-wielding members of the UN Security Council, blocked all attempts to refer the case to the ICC. Instead, they pressured Syria into joining the Chemical Weapons Convention, effectively forcing the regime to destroy its chemical weapons stockpile in the process.

Since then, Damascus has repeatedly denied involvement in chemical weapons attacks on Syrian soil, but documentation obtained by DW suggests that the Syrian regime did not comply with its obligations to dismantle its chemical weapons program in its entirety. The Syrian embassy in Berlin did not respond to a request for comment.

For survivors, the international community has failed to deliver justice.

"They let us down," says Eman, her eyes swollen from weeping. "All countries failed us, especially the Arab nations that would not even open their doors for us to seek asylum. We thank Germany for opening the doors to us and helping us, but they also let us down in the face of Assad's injustice."

And yet, seven years on, the tides may be turning in their favor. Eman and Mohammed are witnesses of a criminal complaint filed in Germany. 

The merits of universal jurisdiction

In early October, a consortium of three non-government organizations filed the complaint with the Federal Prosecutor's Office against unnamed persons with regards to apparent sarin gas attacks in Ghouta in 2013 and Khan Sheikhoun in 2017.

The consortium's motivation was clear — and strategic.

In 2002, Germany enacted the principle of universal jurisdiction for international crimes, such as war crimes and genocide. It effectively brought German domestic law into accordance with the Rome Statute, a treaty that established the ICC that year.

By doing so, Germany extended its jurisdiction over "the most serious crimes affecting the international community as a whole," even if they were not committed within its territory or against its citizens. In Koblenz, the first case accusing Syrian regime figures of systematic torture opened in April as a result of Germany's universal jurisdiction.

That led the Open Society Justice Initiative, the Syrian Archive, and the Syrian Center for Media and Freedom of Expression to file the criminal complaint with the Federal Prosecutor's Office in Karlsruhe, where a war crimes unit had launched a structural probe in 2011 into atrocities committed in Syria.

The war crimes unit in Karlsruhe confirmed to DW that it had received the criminal complaint from the Federal Prosecutor's Office. However, it would not provide further comment regarding the case.

"We are investigating the evidence, and that's all we can say for now," a spokesperson for the unit told DW.

The burden of proof

The criminal complaint provides extensive documentation alongside open-source information that could be used as legal evidence of war crimes committed in Ghouta and Khan Sheikhoun. It included testimonies from at least 50 defectors of the Syrian regime with firsthand knowledge of the country's chemical weapons program.

A vast portion of witness testimony has been corroborated by videos and images taken by people on the ground, including victims. The content was collected and archived by the Berlin-based Syrian Archive, which also undertook the task of verifying the material.

Digital evidence "becomes really important and central to the legal complaint by helping corroborate witness testimonies," says Hadi al-Khatib, director of the Syrian Archive.

Such evidence has been crucial to forming a broader picture of the events, and has supported the findings of the official UN probe into the Ghouta attack. The UN fact-finding mission did not name suspected perpetrators because attribution was not part of its mandate. But it made one thing abundantly clear.

"The environmental, chemical and medical samples we have collected provide clear and convincing evidence that surface-to-surface rockets containing the nerve agent sarin were used," said the UN fact-finding mission in a report less than a month after the attack.

"This is a war crime," said then-UN Secretary-General Ban Ki-moon.

Searching for a smoking gun

Key to the criminal complaint filed in Germany is the diverse array of witness testimony. It includes high-ranking military personnel and scientists at Syria's Scientific Studies and Research Center (SSRC), which was responsible for developing and maintaining the country's chemical weapons program.

Evidence suggests that President Assad's younger brother, Maher Assad, widely considered the second most powerful person in Syria, was the military commander who directly ordered the use of sarin gas in the Ghouta attack of August 2013.

However, witness statements filed with the criminal complaint also indicate that the deployment of strategic weapons, such as sarin nerve gas, could only be executed with President Assad's approval.

According to documentation seen by DW, President Assad is believed to have authorized his brother to conduct the attack.

"We have evidence that [President Assad] is involved in the decision-making. I wouldn't say that we ourselves have proven that, but we certainly have some information that indicates his involvement in sarin attacks," emphasizes Steve Kostas, a senior legal officer with the Open Society Justice Initiative's litigation team.

The documentation shows how Assad's brother Maher would have then given the official order at an operational level. From there, an elite group within the SSRC dubbed Branch 450 would have loaded warheads with chemical agents and the 155th Missile Brigade would have launched the surface-to-surface rockets under direct oversight from Maher.

"We've shown that there was a specific unit called the Branch 450 within the SSRC, which was significantly involved in the planning and execution of sarin attacks," says Kostas. "We've shown the chain of command involved in that unit and its connection to the presidential palace.

To this date, the testimonies describing the chain of command are considered the strongest available evidence directly linking Assad to the use of chemical weapons in Syria.

Culpability at the highest levels?

But is that enough for German prosecutors to issue an indictment? For international law experts, a smoking gun isn't required for an indictment of this caliber.

Throughout history, there have been moments where countries have collectively taken steps to enact justice against perpetrators of mass atrocities, such as the Nuremberg and Tokyo trials in the wake of World War II.

The underlying concept of such nation-driven tribunals is that individuals who form part of a command structure can be held to account for atrocities, even if they did not personally commit them.

Since war crimes are often committed in a system of armed forces, international law recognizes that command hierarchies enable such violations, Robert Heinsch, director of the Kalshoven-Gieskes Forum on International Humanitarian Law at Leiden University, tells DW.

"People who have given orders to normal soldiers or whoever is in charge of launching the attacks can be indicted because of this act of ordering — or even if the person didn't order it themselves but they were aware or should have been aware of these attacks," says Heinsch.

"Because of their function as a military commander, they can be held responsible — and that's very important. This is also incorporated into the German code of crimes against international law, because you would otherwise not be able to hold these people responsible."

In Germany, the law establishing universal jurisdiction has only been used once to convict a perpetrator. In 2015, German judges found Rwandan Hutu rebel leader Ignace Murwanashyaka and his aide guilty of war crimes and crimes against humanity. Murwanashyaka's conviction was overturned three years later and he died while awaiting retrial.

The only other trial that has employed universal jurisdiction to prosecute perpetrators is the case in Koblenz targeting senior Syrian regime figures for alleged torture.

'Maybe it's only the beginning'

In his capacity as Syria's president, Assad heads Syria's armed forces. On several occasions, he has made clear that as commander-in-chief, ultimate authority lies within his office, telling Chinese state broadcaster CCTV in September 2013 that he is "the lead decision-maker in moving and leading the armed forces in Syria."

But other factors are also crucial for a viable prosecution.

Even if federal prosecutors decide to cross that threshold and indict the highest regime figures allegedly involved in the decision-making process, other issues could derail the case, including sovereign immunity, under which an acting head of state is traditionally protected from prosecution.

For those pursuing justice against Syria's top regime figures, the endeavor is shy of a Sisyphean task. But that has yet to dissuade them.

"We know this process will take 10, 20, maybe even 30 years. So we must also try to prepare ourselves for a long term strategy. We know from all of our experiences that this is not something that will be finished within a day," says Mazen Darwish, president of the Syrian Center for Media and Freedom of Expression.

"Maybe it's only the beginning."

Since 2011, Germany's war crimes unit has tasked more than a dozen prosecutors with a structural investigation of war crimes and crimes against humanity in Syria.

Germany is now home to an estimated 600,000 Syrians, the vast majority of whom fled their country to escape the brutal conflict. Throughout their asylum applications, they are frequently questioned about their part in atrocities, whether as victims or perpetrators.

But Germany isn't the only jurisdiction the plaintiffs plan to litigate against the perpetrators of chemical weapons attacks in Syria. The consortium of NGOs plans to file criminal complaints in other European jurisdictions by next year.

"We hope that we can galvanize universal jurisdiction prosecutors to investigate these attacks and to hear evidence that we've presented so that they can build criminal investigation files that will support prosecutions in the future," says Open Society's Steve Kostas.

Longing for justice

Located on the ground floor of a nondescript Berlin building and decorated with little more than a whiteboard, the offices of the Syrian Archive have managed to reflect its founder's ascetic quality. For Hadi, who now resides in Germany, little has mattered more than the pursuit of justice in Syria.

International efforts have focused on combatting impunity in the conflict through transnational approaches. But for Hadi and many other Syrians, the goal remains much closer to home.

"Those mechanisms to ensure accountability are really important … and ensure people understand that justice is not forgotten," says Hadi.

"They are important mechanisms — until justice and a trial can happen in Syria, which would have a very different meaning for all the people there."

Mazen Darwish, a Syrian lawyer and exile living in Germany, agrees.

"This is not justice," says Darwish, who was arrested several times in Syria for his advocacy work. "These are the alternative choices, because one day we will create a respectable transitional justice system in Syria."

Back at Eman and Mohammed's home at an undisclosed location in Germany, the memories of the chemical attack plague their every waking moment. Yet, that despair has not deterred them from the hope that one day the perpetrators of the Ghouta attack will face justice.

"Injustice taught us to be brave. But as much as we have courage, we are weak and what happened in front of me never goes away," says Eman.

"But this is my wish in this world. That they will hold [Assad] accountable — he and all those with him who wronged us and many others, who wronged many children and left so many homeless."

DW's Wafaa Albadry contributed to this report.