New York, United States - When Mahmoud Nowar was released from detention, doctors told his father that he was so withered and malnourished that he would only have survived a few more days of starvation and torture at the hands of Syrian government forces.

The pro-democracy activist and former resident of Yarmouk, a Palestinian refugee camp in the southeast of Syria's capital, Damascus, was beaten, interrogated and locked up with 120 other men and boys in a fetid underground cell for nearly three months in 2013.

I'm not looking for revenge. Justice, for me, means releasing the prisoners who are still dying every day. To stop this hell Mahmoud Nowar, a refugee from Syria

Speaking to Al Jazeera, Nowar said his battered and scrawny body looked like the photos of corpses that were taken by a military police photographer who defected, code-named Caesar. He supports those probing the atrocities committed in Syria, but also speaks of more urgent concerns.

"I'm not looking for revenge. Justice, for me, means releasing the prisoners who are still dying every day. To stop this hell," said Nowar, 33, who fled Syria at the end of 2013 and came to the United States on a Harvard University scholarship in January.

Testimonies from torture victims like Nowar, along with Caesar's 55,000 images and thousands of other documents that have been smuggled out of Syria since 2011 are being collected in an effort to charge and prosecute those responsible.

Efforts towards this goal have been largely thwarted by Russia, which backs the government of Syrian President Bashar al-Assad and has used its veto in the United Nations Security Council to stop the case being referred to the International Criminal Court (ICC).

But Moscow could not block 105 countries in the UN's larger body, the General Assembly, from taking the unprecedented step of bypassing the Security Council and voting in December to open an office to lay the groundwork for future prosecutions.

Within days, the UN is set to name the head of the International, Impartial and Independent Mechanism (IIIM), which will collect and preserve evidence of serious crimes committed in Syria and build cases against those most responsible for them.

A start-up team has already met in Switzerland and is expected to grow to a 50-strong staff based in Geneva this summer. It has secured about half of its $13m first-year running costs via donations from Finland, Germany, Qatar and others.

But there is a catch - the IIIM is really a "prosecutor without a tribunal", said Kenneth Roth, executive director of the pressure group Human Rights Watch. It can build cases, but it does not have a dock for trying defendants.

Instead, the IIIM can pass evidence to courts and tribunals, such as the European courts that are already prosecuting some Syrians accused of war crimes, a UN-backed tribunal or perhaps even the ICC at some point in the future.

There is no shortage of evidence. The Commission for International Justice and Accountability (CIJA), an independent group of lawyers based at a secret European office, has amassed some 700,000 pages of Syrian intelligence and security archives.

Mohammad Al Abdallah, director of the US-based Syria Justice and Accountability Center, has collated some 500,000 pages of official documents, complete with "official seals and stamps" and thousands of videos uploaded to YouTube, he said.

His team has built a database and cross-references images, videos and files. He showed Al Jazeera a video of men being detained and beaten by government forces, and a subsequent video of their charred bodies being found later on the street.

Government documents showed this was part of operations in the area, completing the prosecutor's jigsaw puzzle, he added. "There is clearly proof of the systematic nature of these attacks," Abdallah told Al Jazeera.

Monitors have repeatedly warned of crimes during Syria's six-year civil war, from the poison gas attacks and bombardment of towns that are levelled by Assad's forces to genocidal raids by the Islamic State of Iraq and the Levant (ISIL).

'Policy of extermination'

In February, Amnesty International, a rights group, reported that some 13,000 people were hanged over five years at the state-run Saydnaya prison near Damascus in a "policy of extermination". This month, the US said the government had built a crematorium there.

According to Stephen Rapp, a war crimes prosecutor, the Assad government's alleged interrogations and torture of dissidents are interesting to investigators because they rank as serious and widespread crimes with hard-to-deny evidence.

"With a detention facility, you're talking about the people running those joints, their commanders in military intelligence and a straight chain of command all the way up to the president," Rapp told Al Jazeera.

"There's no problem with the paper trail to Assad."

Evidence of atrocities in Syria is abundant, but there is much dispute over whether war crimes tribunals ease conflicts. Some say they make despots think twice before hurting civilians, while critics say they cause ever-more brutality in desperate bids to keep power.

Jan Egeland, secretary general of the Norwegian Refugee Council, a charity, said "men with guns and power routinely attack" civilians and aid workers in Syria, but they can be scared into better behaviour on the battlefield.

"We need to make those who do wrong sleep less well at night," Egeland told Al Jazeera.

Others say that war crimes tribunals are too easily politicised and ICC-style cases serve the interests of the court's mostly Western backers. In Syria, government forces and the opposition have all used dirty tactics in fighting that has claimed some 465,000 lives, critics say.

In April, Moscow's deputy UN envoy Vladimir Safronkov vetoed the latest Western-backed draft resolution on Syria. He called it "odious and erroneous" and criticised the weak evidence linking Assad's forces to a poison gas attack in Khan Shaykhun, in Idlib province.

Britain, the US and others were not interested in justice for casualties of war, but were instead using global bodies for "geopolitical ends" and creating "additional grounds for regime change in Damascus", said Safronkov.

Moscow is unlikely to change its mind on an ICC referral anytime soon. Assad rejects claims that his forces have committed atrocities. Although the country is divided by fighting on multiple fronts, he is under no immediate threat of losing the war.

Under these conditions, Rapp, Roth and Abdallah agreed there was little hope of quickly creating a Syrian tribunal. At present, they pin their hopes on European courts using "universal jurisdiction" to prosecute Syrian government torturers and others.

According to Amnesty International, France, Germany, the Netherlands, Norway, Sweden and Switzerland are all processing investigations on Syria. Two rebels have been separately tried and jailed for crimes in Syria's war after they left the country and travelled to Sweden.

Spanish authorities have begun proceedings against nine Syrian government officials over claims of the torture and execution of a detained man, in a case brought by the alleged victim's sister, a Spanish woman of Syrian origin. The IIIM could help more prosecutions like this.

Such cases have flaws: they are piecemeal, unlikely to satisfy all victims, and the accused seldom turn themselves in for questioning. This will mean that some cases are dropped, while others may result in convictions of individuals who remain at large in Syria or elsewhere.

While indicting Assad's security chiefs is a distant prospect now, Rapp said, the slow-moving wheels of justice eventually caught up with Chile's Augusto Pinochet and Slobodan Milosevic of the former Yugoslavia.

The endgame to Syria's war is unclear, added Abdallah. Fighting or negotiations could yield a political shift that sees Damascus refer itself to the ICC, or cooperate with a UN "hybrid court", akin to Cambodia's tribunal for members of the Khmer Rouge.

Roth had another idea. "If Russia continues to stymie the ICC, it may then become time for the General Assembly to do what they just did with the prosecutor - there's nothing stopping them from setting up a tribunal as well," he told Al Jazeera.

Follow James Reinl on Twitter: @jamesreinl