Hidden struggle among Syria's rebels
I first met Abu Somer during the early days of the battle of Aleppo in August 2012. Now he commands a Syrian rebel brigade laying siege to a military base near Saraqeb, about 50km (30 miles) to the south-west.
Why did he leave Syria's second city while its destiny still lay in the balance? He is silent for a moment. Then he mutters: "Some Islamic brigades wanted to assassinate me."
Ten months ago, when Abu Somer was among secular fighters confronting government forces on Aleppo's Salah al-Din front, there was no Islamist involvement in the action.
The majority of fighters wanted to overthrow the regime of President Bashar al-Assad and create a secular country in which the power to decide who governs rested in the ballot box.
But that changed and, after what he says were three assassination attempts against him, Abu Somer decided to leave to avoid infighting that would benefit the Assad regime.
He says he tried many times to contact the Islamist brigades to protest, but the answer always came back: "It is the shabiha [pro-government militiamen] trying to kill you, not us."
The potential for violent struggle between Syria's opposition factions was always there, but none of the rebels expected it to play out before President Assad was removed from power.Sharia courts
On my last tour of rebel-held areas in northern Syria, the streets looked very different.
The black-and-white banners representing Islamist factions are now prevalent in most areas, instead of the green flag of the revolution.
Abu Qudama, a Jordanian member of the al-Qaeda-backed al-Nusra Front, commands the Security Brigade in Saraqeb, a collection of Islamist fighters from different factions that enforces rulings of the town Sharia court.
He says the people of Saraqeb supported Islamic rule and demanded his faction's intervention to administer civilian life.
One of the signs of the rising influence of Islamism is the Sharia court. In Saraqeb, the Sharia judge presides in the court, first over a car crash and later over an accusation of assault against another al-Nusra Front commander.
Outside the court, a civilian called Samir has come with a group of supporters to complain about a public flogging administered to his neighbour.
The man had been convicted for allowing his daughter to remarry before her period of enforced isolation had elapsed. For this he was flogged and is now too ashamed to show himself in public.
Samir rallies the crowd, demanding to know who gave legitimacy to foreigners to rule the country and asking whether they would leave after the war ended.
He says he is a Muslim but argues that Syria cannot be governed in accordance with the views of a single sect.
"When you build your house you cannot just stack bricks on top of each other - the different sects and ethnic groups are the cement that holds our country together," he says.
On the walls around us, there are slogans like "Down with the Sharia court in Saraqeb", "Who installed you as ruler upon us?" and "Where were the Islamists when the secularists started the revolution?"
It is reminiscent of the graffiti that used to appear secretly when Mr Assad's forces still controlled towns like this.
Like under the previous regime, popular demonstrations are banned in Saraqeb, although the security brigade says this is to protect civilians from the regular shelling of the town by government forces.Islamic caliphate
Tensions between different factions were also on show when I sat with some fighters who had just stormed a loyalist checkpoint in a rare joint operation.
During a conversation about their vision of a future Syria, Abu Dujanah, an Iraqi-American who had recently joined the al-Nusra Front, expressed anger to hear fellow Sunnis talk about a parliamentary democracy with legislative elections.
For him this was the chance to establish an Islamic caliphate envisioned by the Prophet Muhammad in Greater Syria,
Would he return to the US if the regime fell? He answered no, he would continue his jihad until the "liberation of Palestine" from the Israelis.
Another fighter, Abu Youssef, joined us saying he was a US citizen who had come from Qusair, which was retaken by government forces early in June.
He blamed the defeat on fighters who kept themselves remote from religion and God, and he especially condemned members of al-Farouq brigades who spent the day fighting and the night watching TV and singing.
"When you come back you don't feel you are on the battlefield, you feel like you are in a party," he said.
If the future of the struggle between the Syrian regime and opposition groups seems bleak, these scenes show the other hidden struggle between armed opposition groups with different agendas for the future state.
Since the BBC Arabic documentary The Battle for Syria's Courts was broadcast, Abu Qudama issued a statement saying he and al-Nusra will no longer run the courts. The Sharia courts however, are still functioning and are run by other members of the Security Committee.