Syrians gather at a graveyard during the funeral of a man killed by a shrapnel Feb. 28, 2012, in the Syrian town of Qusayr. (Gianluigi Guercia/AFP/Getty Images)

This week marks the fifth anniversary of the start of the Syrian war, a conflict that began as a peaceful revolt but gradually devolved into horrible bloodshed. As with any anniversary, there will be an accounting of sorts Tuesday – an attempt to ascertain what has actually happened in half a decade of conflict and chaos.

That accounting can be a frustrating experience, however, because a key part of the information is simply not there. Five years into the brutal Syrian war, the exact death toll of the conflict is unclear. At best, all we have are estimates.

Perhaps the most widely cited of those estimates come from the United Nations, who last summer suggested that more than 250,000 people had been left dead by the war. However, the convoluted backstory behind the U.N. estimate is indicative of how difficult a task counting the dead is. Initially, the U.N. had semi-regularly offered estimates for the death toll in Syria until July 2013, when it abruptly stopped.

At the start of 2014, Rupert Colville, a spokesman for the U.N. Office of the High Commissioner for Human Rights (UNHCR) who had been releasing the numbers, told reporters that the organization could not offer a reliable figure for the death toll, and that due to doubts about the accuracy of the information they were presenting, the U.N. would not release new death tolls. However, in August 2013, the U.N. apparently reversed that decision, and released a new estimate of 191,369 – a figure that Colville cautioned was "indicative" rather than "gospel truth."

UNHCR has only limited access to Syria. To make its estimates, it has had to rely on the work of third-party groups in Syria who make their own death counts for the country. Perhaps the most widely cited of these groups is the Syrian Observatory for Human Rights (SOHR), a group ran by Syrian activist Rami Abdulrahman from his home in Coventry, Britain. Abdulrahman has said he uses a network of hundreds of volunteers based in Syria to help collect and corroborate his information.

In late February, SOHR updated its death toll to conclude that it could find 271,138 documented deaths since the beginning of the Syrian war, of which 122,997 were civilians. In total, SOHR estimated that 370,000 people had been killed in the conflict.

SOHR are not the only group following the Syrian death toll, however. Another group is the Violations Documentation Center (VDC), a group who currently have recorded 131,919 deaths in the conflict – a figure they acknowledge may be low as they are not able to record the deaths among those fighting for the Syrian regime. Another group, the Syrian Center for Policy Research, estimated in December that around 470,000 Syrians had died in the war.

Varying death toll estimates are certainly not limited to Syria. Estimates for the number of dead in the post-2002 Iraq war have ranged from 242,000 (from the Iraq Body Count project) to 655,000 (from an especially controversial 2006 Lancet study). If you go back further you can see that many historical conflicts offered vague or disputed death tolls: Estimates for the number of Germans who died in World War II can vary between 4 million and 5.3 million, for example.

However, the Syrian conflict has taken place in the era of social media, raising both the ability of groups to record deaths but also the expectations of accuracy. The differing figures from various groups have also lent credence to the idea that the figures are politically motivated, a fact made worse by the difficulty in fully explaining how the figures have been reached (SOHR, for example, refuses to share its methodology).

In some ways, the details matter more than the big picture in the death toll, but again, the details are divisive. The exact number of deaths that can be attributed to the forces of Bashar al-Assad versus the rebels is unclear, for example: Most of the estimates suggest that Assad's forces are responsible for the majority, but few, if any, groups loyal to Assad publish their own estimates. “Nobody could double-check these figures, or triple-check them; we are not sure about these figures,” Syria’s U.N. ambassador, Bashar al-Jaafari, told Foreign Policy magazine recently, suggesting that while the death toll was high in Syria, the Assad regime was primarily a victim rather than a perpetrator.

For outsiders, this problematic accounting is deeply worrying. Many observers to the war hope that at some point something approaching justice can be found in Syria when the fighting finally stops. A decent understanding of what actually happened during the war is needed for that to happen.

But the disputed death toll also spells out a far more immediate and real problem for Syrians. Many simply don't know what happened to their loved ones. And many never will.

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