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After news spread of a massacre in the village of Haswiya in central Syria on 15 January 2013, two accounts of what happened emerged.

Syrian security forces who escorted the BBC team to the site of the killings insisted the 100 deaths were the work of the al-Nusra Front - Islamist militants fighting alongside the rebels.

However, activists said pro-government gangs, known as Shabiha, were to blame.

Since then, the BBC has been trying to piece together the two narratives. Was this sectarian bloodletting by the state-sponsored militia or was it an attack by militants on a village that was supporting the government?

Security forces view: The case against the Islamists

According to the Syrian security forces, the victims were killed by militant Islamist group the al-Nusra Front in revenge for their support for the government.

An army commander told the BBC how hundreds of men from the organisation - a feared and a secretive rebel-aligned group known for members' black clothing and long beards - came across the fields from nearby Talbisah on the morning of Tuesday 15 January.

Continue reading the main story “ Start Quote There were houses that were burnt with whole families inside them. There are children who were burnt in the arms of their mothers” End Quote Haswiya villager

The group was able to approach the village because there were no checkpoints to the north of the village, he said.

Asked why a Sunni rebel group would attack a Sunni village, the commander replied: "Because they refuse to house them, to support them. This village is supporting the government."

Others in the village - now reportedly in the hands of anti-government forces - confirmed the army's account. They described how the men - strangers wearing army trousers and black jackets - went on a killing spree.

"They didn't allow us to do anything. We couldn't seek help, they put the guns to our heads. They came from the fields, " one woman told the BBC.

Another villager told how more than 100 people lost their lives.

"There were houses that were burnt with whole families inside them. There are children who were burnt in the arms of their mothers - down in the fields," one couple said.

According to the army, soldiers only entered the village later in the afternoon after villagers raised the alarm. They told the BBC it was then that they cleared the area and took away the bodies.

Anti-government view: The case against the pro-government militia

One woman, who spoke to the BBC off-camera, out of earshot of military minders, said Syrian soldiers were in the village that day, and that some had apologised that "others acted without orders".

Asked why the soldiers didn't protect the villagers, she said: "They were together, they are dressed in the same uniform. They were mixed."

Continue reading the main story Haswiya is a microcosm of a country being ripped apart by war. It's not easy to get access to the evidence of a growing catalogue of war crimes and crimes against humanity. But seeing the grisly remains of even one massacre underscores a shocking savagery. A UN Commission of Inquiry has just released what's being described as the most comprehensive and factual account of how the Syrian war has been waged over the past six months. Its contents are grim. "We're talking about hundreds and hundreds of major violations," Vitit Muntarbhorn, one of its four commissioners, told me. They've been able to compile evidence of six massacres committed by government forces in this period, two by the armed opposition, with many others being investigated - including Haswiya. As violence escalates and spreads, individual atrocities are being eclipsed. But every massacre leaves behind a traumatised and terrorised community. Every one of them matters.

The Syrian Observatory for Human Rights (SOHR), a UK-based activist group, blames pro-government gangs, often referred to as Shabiha.

It described how some victims were "burnt inside their homes while others were killed with knives" and other weapons wielded by gunmen loyal to President Bashar al-Assad.

SOHR said it had also received reports that whole families were executed - one of them made up of 32 members.

Although accounts of the sequence of events vary, a number of sources describe how security forces entered the village around midday.

They describe how buses carrying the military drove to the outskirts of the village before soldiers disembarked and blocked all routes in and out.

It is claimed that soldiers then went from house to house conducting what appeared to be arrest operations and took a number of people away for questioning on the outskirts of the village. Some were later released.

Some sources tell how gunmen then came back into the village an hour or so later and began killing - executing people and burning their bodies. Online testimony identifies the attackers as Shabiha and some of those accused of carrying out the killings are even named on social media.

Others have also questioned why the atrocities, which villagers said took hours, weren't stopped by those at the military base, which was located just around the corner.

Forensic pathologist's view

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Forensic pathologist Professor Derrick Pounder, who watched the BBC's footage in detail, confirmed that multiple victims appeared to have been shot in their homes in the village. There was also evidence of the burning of buildings and corpses as well as robbery, he said.

The bloodstain evidence suggested that the scene was a couple of days old when the BBC team arrived, he explained, and there were also signs of disturbance at the scene, suggesting one or more people had returned after the initial attack.

Watching the footage from the two compounds, Prof Pounder concluded most of the victims had been shot before being burnt.

Blood trails and bullet holes in one kitchen also appeared to show three people - possibly in a crouching position - were shot and dragged away shortly after their deaths.

Prof Pounder also suggested that smoke from the fires would have drawn attention to those carrying out the killings - unwise in a combat situation. The nature of the killings therefore suggested a "sense of impunity on the part of the perpetrators", he said.

In addition, there appeared to be little benefit in torching properties or bodies, he explained, other than to terrorise the population, since the fires did little to conceal the crimes that had been committed.

One possible reason why some bodies were left behind while others had been removed could have been that the fires were still smouldering at that time, Prof Pounder said.

Produced by Lucy Rodgers, Kate Benyon-Tinker, Chris Lawton and Salim Qurashi