The murder of a boy accused of blasphemy has come to symbolise concerns about the power of Islamist radicals in Syria's armed uprising. Paul Wood reports from Aleppo on how Sharia is spreading in rebel-held areas.
Mohammed Qataa's mother wanders the streets of Aleppo looking into strangers' faces as she tries to find her son's killers.
She knows she would recognise them. She was looking right at them when, in front of a dumbstruck and terrified crowd, Mohammed was shot dead, accused of blasphemy.
She remembers Mohammed as a happy, dutiful son, well known and well-liked in the Shaar neighbourhood where the men of the family scrape a living with a coffee cart.
He was 14 years old, but with no schooling possible because of the war he was usually to be found on the busy main thoroughfare through Shaar, selling the thick, sweet coffee they prefer here.
One day last month, someone asked him for a free cup. "Not even if the Prophet himself returns," he had replied, laughing. That remark was a death sentence.
It was overheard by three armed men. They dragged him to a car and took him away. Half-an-hour later, a badly beaten Mohammed was dumped back in the road by his cart.
The men, showing no fear that anyone would question what they were doing, summoned a crowd with shouts of "Oh People of Aleppo. Oh people of Shaar." Their bellows alerted Mohammed's mother.
Recalling what happened next, she buries her face in her hands and weeps.
"One of them shouted: 'Whoever insults the Prophet will be killed according to Sharia'," she told me.
"I ran down barefoot to the streets. I heard the first shot. I fell to the ground when I got there.
"One of them shot him again and kicked him. He shot him for a third time and stamped on him.
"I said: 'Why are you killing him? He's still a child!' The man shouted: 'He is not a Muslim - leave!'"
After the murder on 10 June, pictures of Mohammed's body went viral on Facebook and Twitter in Arabic.
He had been shot in the face, a hole where his nose and mouth should have been.
There was an outcry. It was claimed that the killers were from the main group linked to al-Qaeda here, the Islamic State of Iraq and Syria. Suspicion also fell on the Nusra Front, the biggest Islamist organisation in the uprising.
Both issued statements condemning the murder, as did almost all of Aleppo's rebel brigades, and the city's main Sharia court.
We met a judge there, a 26-year-old Islamic scholar barely out of university, with a wispy beard and round glasses.
He told me the men were regime militia, "shabiha", trying to foment trouble between jihadis and other fighters.
I found that explanation rather convenient, along with the disavowals of the murder by the two Islamist groups linked to al-Qaeda.
Would regime thugs really have risked entering the heart of opposition-held Aleppo to abduct a boy - and then have returned half-an-hour later to kill him in the street?
The family say the evidence is confusing. The men spoke the classical Arabic of the Koran, yet made simple mistakes. They made the odd statement that blaspheming against God could be forgiven but insulting the Prophet was a capital offence.
The four looked like jihadis but stopped to buy a packet of sunflower seeds. People explained that the truly pious would not eat sunflower seeds because they take so long to shell - and the Prophet said not to waste time.
But though the family don't know - or are too afraid to say - which armed group is to blame for Mohammed's death, they maintain that the rebel authorities bear ultimate responsibility.
"We have no freedom left," says Mohammed's older brother, Fouad.
"We had it when the rebels first took over in Aleppo but now we have nothing. What we have instead are countless [Sharia] committees, each following its own interpretation of religion."
Aleppo's main Sharia court has taken pains to stress that though Mohammed Qataa's murderers said they were acting in the name of Islam, the killing was un-Islamic, a criminal act.
But whatever the killers' real motives - whether a brutal trick by the regime or a cruel and extreme interpretation of Islam by jihadis - it is also true that Sharia is spreading in rebel-held parts of Syria.
A documentary team from BBC Arabic went to the northern town of Saraqeb to follow the work of the Sharia court there, gaining extraordinary access over a period of six weeks.
The court is run by a 27-year-old former preacher, Sheikh Abdullah Mohammed Ali, who hands out sentences dressed in Afghan-style shalwar kameez, a Kalashnikov at his side.
Four men convicted of trying to steal a taxi driver's car are brought before him. Although admitting their guilt, they claim to be members of a rebel brigade.
Sheikh Abdullah tells them their weapons will be confiscated and they will not be allowed to be part of any armed group in future.
He swiftly decides that the sentence will be a public flogging. The men are driven to the centre of Saraqeb for sentence to be carried out. The instrument of punishment is an electrical cable.
Sheikh Abdullah takes a megaphone to address a small crowd that has gathered.
"In the name of God," he says, reading out the names of the four prisoners standing in a row. "Fifty lashes for the leader of the gang. Forty for each of his men."
He declares: "God's law is the best protection for the weak."
The first of the prisoners is forced to his knees, a man on either side of him holding his arms. When it starts some of the crowd chant, "The Prophet is our leader". Others just count the lashes.
Afterwards, Sheikh Abdullah explains to the documentary crew that the punishment was actually quite lenient. They had been convicted of highway robbery. The normal penalty for that is death, he says.
"In wartime, punishments according to Sharia are suspended until peace returns," he says.
"Now, we are at war. We must concentrate on fighting the regime's army. Full punishments will be enforced as soon as the regime falls and an Islamic State is declared."
'Alternative to chaos'
The uprising's rural, conservative and religious supporters approve of Sharia's harsh penalties.
So too, perhaps, do many of those afraid of the criminal anarchy, the looting, killing, kidnapping and theft, that has become an everyday fact of life in rebel-held areas.
But many in Saraqeb are dismayed by the rise of the Islamists. There have been small street protests in the town against Sharia.
"We did not hope for what we have come to today," said Lyas Kadouni, an activist interviewed by BBC Arabic.
"The names of [rebel] brigades tell you how people think now - names like 'Lovers of the Prophet Brigade' and so on. It is not necessary to throw religion into every corner of your life. This is killing our revolution."
Painfully earnest, Lyas Kadouni wants to tidy up Saraqeb's streets. "The most important thing is to practise the duties of citizenship," he says.
"We have to show… we have an alternative to chaos."
He says he is "100% certain they [foreign jihadis] will disappear". It could take a month, two, or three months, he says.
But the influence of relatively secular activists like Lyas Kadouni, always marginal, is waning still further.
Almost two years after peaceful protest became a civil war, they are still painting murals and handing out leaflets. Others, meanwhile, are taking power at the point of a gun.
Things are not going entirely the Islamists' way, however. They have split and split again over the question of whether to unify with al-Qaeda. There is also a bitter ongoing battle with elements of the Free Syrian Army.
While most fighting on the rebel side are Muslim, many of those do not want a religious state.
The commander of one such unit told me the Islamist Nusra Front had sent a suicide bomber to one of his positions, killing a dozen of his men. Then his brother was kidnapped by the jihadis. After paying a ransom of tens of thousands of dollar to get his brother back, he would now seek revenge.
"There will be nowhere for them to hide."
Even as government forces sweep into previously opposition-held towns, the rebels are fighting amongst themselves, hardline jihadis against the relatively secular FSA, a civil war within the civil war.
The battle, though sporadic, seems just as bitter as that against the regime.
Its outcome will determine what kind of state Syria will become if the rebels win. In the meantime, though, Sharia justice is the only kind available in many parts of Syria.