On the third floor of a nondescript office block in downtown Copenhagen, about 2,500 miles from Damascus, a server gently hums. Its 600,000 gigabytes of data is comprised of thousands of photographs of men, women and children, witness accounts, ages, causes of death, place names, military ranks and weapon types.

The database holds the story of Syria’s slide from authoritarianism into a civil war that, in the course of eight long years, has cruelly morphed into an international conflict with a scarcely imaginable human cost. This memory bank may also amount to the best hope many Syrians have of getting justice.

The database is owned by the Violations Documentation Center in Syria (VDC), a non-governmental organisation founded by the lawyer Razan Zaitouneh, a Syrian human rights activist who was well-known even before the revolution erupted in 2011.

As Bashar al-Assad clamped down on the initial protests and the opposition started to fracture, with new players emerging, Zaitouneh wanted to record every breach of international humanitarian law within the Geneva conventions, Hague conventions, relevant treaties and case law. From imprisonment to torture, murder and kidnap, everything was to be marked. The victims were to be identified wherever possible and the perpetrators, no matter their allegiance, sought out and registered.

Forced in 2012 to flee her home town of Damascus fearing discovery by Assad’s regime, Zaitouneh moved to Douma, six miles north-east of the capital. There, the 36-year-old was abducted on 9 December 2013 from her home by the Jaysh al-Islam, an Islamist militia group, along with her husband, Wael Hamadeh, a fellow lawyer and poet, Nazem Hammadi, and Samira al-Khalil, an activist previously imprisoned for her views by the regime of Assad’s father, Hafez al-Assad. That December day was the last time the so-called Douma four were seen. But their careful forensic documentation has been continued by others.

The jigsaw pieces stored by the VDC in Copenhagen will not ever offer the satisfaction of a complete picture. The centre’s 35 paid staff in Syria and its huge network of volunteers do their best to have eyes and ears in all communities, both in opposition areas and the growing territory controlled by Assad’s regime.

The testimonies and raw data are sent to a team of 15 legally trained verification officers peppered around Europe, who use their larger networks and personal contacts in Syria to refine what they receive and demand more information before sending it on to those inputting it in the database. But the information coming from Islamic State-held parts of Syria remains sketchy and often second-hand due to the dangers of operating there. The database is fluid, updated as fresh information arrives from witnesses, sightings in prisons, medical records, victims’ families or even Imams performing their daily burials.

It is estimated that more than 500,000 people have been killed in Syria as a result of the war. The VDC has documented 188,957 of those deaths and its records suggest 77% were potentially killed in contravention of humanitarian law by the Assad regime. A further 12% of the documentation relates to deaths by armed opposition groups, 4% by Islamic State (Isis) and the extremist Nusra group, 3% by the Russians, and 1.4% by the US-led international coalition. Turkey and the Kurds, along with other peripheral actors, are believed to be responsible for the rest.

Two-thirds of the documented deaths were of civilians. In the early years, arrests, torture and executions made up the bulk of the data. Today, the VDC mainly documents shelling and barrel bombs dropped by helicopters filled with high explosives, shrapnel and oil. The targeting of hospitals and bakeries in opposition-held areas is a notable trend, particularly since the regime’s capacity was improved by the arrival of the Russians. Of the 804 deaths documented in April alone, 420 were named and 384 registered as unknown. The VDC records the causes of death as: 127 by aerial attacks and barrel bombs, 105 by firearms and snipers, 103 by tanks, cannons and mortars, 85 by chlorine, 66 by landmines and car explosives, 10 by torture in Syrian government detention centres and two by torture while in the hands of kidnappers.

This year, Husam Alkatlaby, 36, the human rights activist who took over from Zaitouneh as the VDC’s executive director, received upsetting news, but news that also gave him reason to continue. “When Jaysh al-Islam left Douma for the last time, we were able to receive fresh information about Zaitouneh,” Alkatlaby says. “We can’t say for certain, and we still have hope ... The analysis we have for now indicates that she may not be alive, but we are still working to uncover her fate and to legally prosecute those responsible ... We have lost 12 now, including the four colleagues kidnapped in Douma.”

At the same time, the VCD has signed, along with 28 other Syrian NGOs, an agreement to share information with the UN’s international impartial independent mechanism (IIIM) for prosecuting those responsible for the most serious crimes. The UN’s security council members, in particular Russia, has been accused of blocking the building of prosecutions. The new vehicle offers a chance to circumvent the Kremlin and arm national courts with the evidence they need. “The main goal for me and the team is to keep a record for the next generation,” Alkatlaby says, “but there is a concrete result that we are trying to achieve: to build criminal cases, to hold people to account.”

Alkatlaby, whose parents were in Hafez al-Assad’s prisons for almost the entirety of his childhood, left Syria in 2008 for the Netherlands after friends from universities in Aleppo and Damascus were arrested. In recent months, the VCD has been helping prosecutors in Germany and France to piece together the activities of Syrians in their sights, and the chains of command of military groups.

But Alkatlaby says: “I believe we have to work on the high-level perpetrators. From what we understand the IIIM is interested in building the big cases, not the individual cases. We believe that justice will not make all the perpetrators accountable but what is most important for justice is to get the high level of the opposition, the generals, the close circle around Assad, and Assad himself. That is what we are looking for.”