ALEPPO, Syria (Reuters) - Blindfolded, shuffling along in his slippers, the skinny young man is dragged across a rebel base in Aleppo by armed fighters who slap his back, head and face.
One of a handful of men held captive in the former school by rebels who control much of Syria's biggest city, he disappears down a flight of stairs to the basement, from where sounds of beating and screams emerge.
The 20-year-old man is being held because of a complaint of domestic assault, rebels say, alongside petty criminals and suspected members of the shabbiha militia which supports President Bashar al-Assad.
The fighters say they are trying to impose the rule of law over the areas they control, filling the vacuum left by the collapse of local authority and keeping public services running.
But not everyone in Aleppo and its rural hinterland is happy with the Free Syrian Army rebels, some saying their vigilante operations are often barely disguised vendettas and that they are arrogant and interfering.
"If they don't like the actions of a person they tie him up, beat him and arrest him," said a man who identified himself as Abu Ahmed in the town of Azaz, north of Aleppo.
At the Aleppo base, rebel guards escort a series of limping, blindfolded men to the bathroom throughout the day, one man clutching his stomach in pain after a beating session.
Abu Zaher, a 40-year-old commander and administrative leader of the fighters at this base, says his men are working to maintain order across their area of control.
"We are not just a fighting army," he said. "We are also a group with a vision for reform, we want to bring back morality and civilization to our country."
Military commander Abu Ali said the rebels "organize flour to be delivered to the ovens to keep the flow of bread baked for the neighbors, and we deal with domestic issues between couples who come for our protection."
"We fight petty theft in the streets to keep thieves away."
A stream of people walk through the entrance of the base during the day with a range of requests - donations for fuel, help rebuilding a house, requests to release cars confiscated by the police for traffic violations.
Abu Ali said they had also tried to keep salaries flowing to the cleaning services in the city to pick up trash.
"We are trying to control the situation so that when Assad falls completely there is little chaos," Abu Zaher said. "There are those carrying weapons and pretending to be part of the Free Syrian Army, but who are in fact thieves."
"We have caught men who fill up fuel cans with water and sell it to people as though it is petrol," he said, adding that his men dispense Sharia (religious law) against thieves.
Many of those inside the basement prison are accused of being members of the shabbiha, the pro-Assad militia. Their confiscated weapons sit in a pile in Abu Zaher's office.
Abu Ali said that many of those they catch are released, if they agree to defect to the rebels or can prove they were forced to work against the revolution.
"We caught this guy ordering people at a protest not to chant against Assad," Abu Ali said of the skinny man, dressed in jeans with a mop of curly hair, who was blindfolded and beaten as he was walked across the base.
"He's a shabbiha, but he now says he has reformed and wants to be part of the Free Syrian Army so we're letting him go."
But those found guilty of killing civilians or rebel fighters will be sent to "courts" in Azaz to be judged by the top commander of the Amr bin al-Aas brigade, identified only as Ahmed.
"We use Sharia (Islamic law) to judge our prisoners," Ahmed says in Azaz. "We use a number of judges who are have studied Islamic law and a number of witnesses and judge them accordingly."
"The Islamic ruling for the killer is that he must be killed - so only those who we know have murdered people in this war are shot dead wherever they stand."
The growing clout of the rebels, and signs of rivalry and infighting among them, have alarmed some residents.
"The Free Syria Army is causing us headaches now," said Abu Ahmed, who works with journalists in Azaz. People the rebels don't like are beaten and arrested, he said.
"Personality differences between brigade members are being settled using kidnappings and force. They are self-righteous and we are not happy about it."
He said that on Friday they heard of a man from the town who was taken hostage because he was selling vegetables to a number of Kurds near the Turkish border.
"Because the Kurds didn't stand with us in the revolution and the Free Syrian Army doesn't like them, they decided to arrest him and also asked for a ransom of 25,000 pounds ($400) to let him go."
Abu Zayd, a 22-year-old law student, said the rebels were interfering in Azaz. "They started bossing us around in our neighborhoods," he said.
"They would try to organize the bread lines but then would let their armed friends cut ahead of the civilians in the line, and use their connections within the army to give each other preferential treatment," he said.
"That's why civilians are very focused now to send a message to the Free Syrian Army that we appreciate their work but they need to keep away from our civilian life. If they don't, we will keep taking to the streets against them."
Editing by Dominic Evans and Tim Pearce