The hope must be that criminal justice will one day close in on Syria’s murderous dictator Bashar al-Assad, his henchmen and his enablers. And on that front, there’s been some good news recently: the arrests in Germany and France of three Syrian intelligence officials suspected of torture were groundbreaking. This came on top of the issuance of warrants and the filing of dozens of criminal complaints in a number of European countries, including Sweden and Austria.

It may take time, and the odds may currently look slim, but criminal investigators will eventually work their way up the chain of responsibility to incriminate Syria’s tyrant for the slaughter of his own people for almost eight straight years. Some very motivated lawyers and activists are preparing for the day when those who have perpetrated crimes against humanity in Syria will be held accountable. And it’s in Europe that those efforts are starting to yield the most notable results.

To understand why, think about the hundreds of thousands of Syrians who reached the continent after fleeing the nightmare in their homeland. Many can testify about crimes and help to document them. Members and cronies of the Assad regime have also long taken advantage of Europe as a holiday destination and a place to store assets. And several European countries, not least Germany, accept the notion of “universal jurisdiction”, which allows national courts to investigate and prosecute those responsible for mass crimes even if they were not committed on that country’s territory, by one of its nationals or against one of its nationals.

It’s true that geopolitics have gone Assad’s way since Russia and Iran intervened forcefully to prop him up. Russia made sure the UN was crippled in any attempt to stop the bloodshed or refer Syria to the international criminal court. The US has failed the Syrians by its inaction in the face of mass atrocities. Europe has too. Meanwhile, much of the talk today centres on Islamic State losing its last, shrunken stronghold, and on Trump pulling out US forces. And of course, there are vivid debates in our democracies over what to do about “our” nationals who fought alongside Isis or were lured to Syria by the deadly cult. Almost forgotten in all of this are the long-suffering Syrians themselves – the children suffocated by sarin gas and other chemical weapons, the torture chambers, the forced disappearances, the cities and neighbourhoods subjected to Scud missile attacks and barrel bombs dropped indiscriminately.

So those arrests in Germany and France mattered immensely. One Syrian refugee in Europe – who said he recognised one of the arrested men as his torturer – reacted to the news with these words: “I cried, but with a smile on my lips. It made me tremble for hours … I can now finally say that the impunity Assad’s agents have benefited from in Europe is over. The hope has now grown that Assad himself will one day stand trial.”

Prosecuting the authors of mass crimes is no panacea of course: it would have been much better to prevent them. But from the postwar Nuremberg trials to the 1990s international criminal courts set up for the former Yugoslavia and Rwanda, we know from survivors and the families of victims how important it is that the horror stories are told, that witnesses are heard, and that fundamental principles enshrined in human rights conventions are not ignored. We know also that something of our own integrity, as distant onlookers, is at stake. When future generations look back at an era in which an estimated half a million people were butchered and millions made homeless by one despot’s determination to cling on to power, they will ask: “What did you do?” Since 2011 Syria’s killing fields have been the vortex into which the principle of “never again”, stated so often after the second world war, has disappeared.

Seeking justice for Syrians is no doubt a marathon, but if history teaches us anything, it is that massive human rights violations must not be left unpunished – however long it takes to deliver justice – and not just because prosecutions can act as a deterrent against further slaughter. Relentlessly collecting evidence and establishing the facts are central to preventing history from being rewritten by those who will be tempted to deny such crimes ever took place. The Khmer Rouge trials in Cambodia were held two decades after the genocides. Pinochet was arrested eight years after his dictatorship ended in Chile. Slobodan Milosevic died in jail, not in a palace. Yes, these are difficult times for international justice, but if no international court can help Syrians to seek redress, then national courts can – and must.

After those arrests in Germany and France, I called Catherine Marchi-Uhel, a former French judge who heads a UN investigative mechanism set up in 2016 to prepare criminal case files on Syria. Will Assad ever be prosecuted, I wondered. The answer was “perhaps”, and not just Assad, because the UN will look into the authors of all crimes in Syria, including Isis and Syrian rebels. But Marchi-Uhel’s key message was this: international justice will find a way. “The situation will not for ever remain blocked,” she insisted. “We must have that vision.”

Her team needs more staff and resources – it needs Arabic speakers, analysts and tech experts for “digital evidence management”. So here’s a call-out: if you care, support the justice teams. They’ll reach their goal. An immense body of evidence is already available, not least because the Syrian regime has kept sinister registers of its misdeeds. Documents have been smuggled out. There is a mountain of metadata to search through to establish “the chain of custody”. And at the very top of that mountain sits Assad. Remember, he’s only 53 years old.

• Natalie Nougayrède is a Guardian columnist