One alleged crook, however, has two black eyes.
"I flipped my motorcycle," he said, speaking within earshot of his captors.
An accused regime informer has a bruised face and red stripes on his arm, as if he's been lashed with a cord.
"I fell down," he said.
The Al-Bab prison is one of the many lockups rebels fighting against Assad's regime have set up after seizing areas from government forces.
These facilities report to no national or regional authority, causing concern among rights groups and leading to a wide range of practices.
One badly bruised captive told Human Rights Watch he'd been blindfolded and beaten daily for three weeks. Elsewhere, reporters from The Associated Press saw former regime soldiers frolicking in a swimming pool with their captors.
It is impossible to determine the number of rebel detention centers, but interviews with rebel commanders, activists, captives and human rights researches in north Syria plus visits to three facilities provide a window into the issue.
Little evidence has surfaced that rebels are practicing the widespread, institutionalized torture that human rights groups accuse Assad's regime of. But many prisoners bear bruises and scars from beatings and lashings.
A number of rebel groups acknowledge sending prisoners believed to have blood on their hands to the firing squad. Others realize the living are worth more than the dead and seek "blood money" from captives' families or try to exchange them for rebels held by the regime.
The captors also vary. Running north Syria's largest known rebel prison, in the town of Marea, is a barrel-shaped former truck driver nicknamed "Jumbo" who has a bullet lodged in his head from a gunfight with government troops. Others are run by civilian councils of lawyers, teachers and Muslim clerics who administer a mix of Syrian and Islamic law.
The lack of oversight worries human rights groups.
"It is extremely important that the opposition leadership send a strong message that the kinds of abuses we've seen are not acceptable and that those committing them will be held accountable," said Anna Neistat of Human Rights Watch, who is researching rebel prisons.
More than 17 months of unrest in Syria has killed more than 20,000 people, anti-regime activists say. The conflict has recently descended into a civil war between Assad's regime and rebels seeking to overthrow it.
Assad blames the violence on foreign-backed terrorists seeking to weaken the country.
While neither side appears to be approaching victory, rebels have recently pushed the army from a number of towns in the country's north, leaving them in charge of services like distributing fuel and bread and running prisons. Their fractured approach to administering justice shows how far they are from forming an alternative national government should Assad's regime fall.
North Syria's two largest prisons are run by the Revolutionary Council of Aleppo and the Countryside, which is closely linked to the area's largest rebel grouping, the Islamist Tawheed Brigade. The group holds hundreds of prisoners.
The AP was denied access to the group's main prison in Marea, north of Aleppo. But Neistat of the New York-based Human Rights Watch interviewed two prisoners in private during a visit this month. Both said they'd been beaten on the soles of their feet practice some rebel leaders say is permitted by Islamic law, an idea some Muslims dispute.
The improvised nature of the rebel lockups is clear in Al-Bab, 45 kilometers (28 miles) northeast of Aleppo.
Rebels took control of the city in a battle last month against regime forces holed up in the post office. After some fled, rebels stormed the building, throwing the dead bodies of government soldiers from the roof.
After the regime's withdrawal, local leaders formed a 12-person council to run the city's affairs. They opened the prison in the elementary school.
About 60 people have been through the prison this month, said Mohammed Nouh, the head guard. A prison office collects testimony from residents, and a judicial council of lawyers and Islamic clerics reviews cases. Most people are released in a few days, Nouh said.
The 10 alleged criminals in the prison one recent afternoon had all been caught in the last week, Nouh said. Each had a mattress and a pillow and access to a toilet behind a curtain down the hall. The guards brought plastic razors so the men could shave.
Nouh said the prisoner with the bruised head and arm was a regime spy.
"Lots of people said he's an informer, that he was giving coordinates to the regime," he said.
During an interview away from the guards, Mohammed Abeid, 42, said he'd been arrested because he worked for a government company.
"They arrested me because they say that I belong to the regime," he said. "It's not true."
He said he had not been abused, had eaten well and spoken to the judicial committee, which had yet to decide his fate.
The town's other lockup is a bare room in a former government agriculture office that now houses a rebel brigade.
Fifteen men surrendered to the brigade during the post office battle, and 10 were released after rebels determined they hadn't killed anyone, said Omar Othman, the group's commander.
Interviewed alone, the five remaining captives said they had not been abused and ate regularly, though they worried the rebels were using them to raise money by demanding ransom.
They had been divided by sect. Othman said three former police officers all Sunni Muslims like most of the rebels had been exonerated and would go home soon. The two others were military security officers and Alawites, members of the religious minority of Assad and many in his regime.
While denying that sectarianism influenced the group's decisions, Othman said the two men had repressed anti-regime protests and that the regime would want them back.
"We want a prisoner exchange, nothing more and nothing less," he said.
Other groups too have used captives to their advantage.
A rebel group in the Aleppo suburb of Kafar Hamra held 13 captured soldiers in their rural, three-story villa. While technically prisoners, the captives moved about freely, ate with the rebels and swam with them in the villa's pool.
All were Sunni Muslims in their early 20s who had been doing their mandatory military service when caught. Even when interviewed alone, they said they ate better with the rebels than they had in the army and trusted them to get them home.
"Why would I flee?" asked captive Mohammed Kilani, 22. "They are feeding me and giving me cigarettes and we play soccer together and they tell me they'll get me to my family."
A while later, the uncle of one of the captives paid the rebels $750 to release his nephew, a captured conscript from Damascus.
"It's fine," Jihad Khalid said of the money. "If they'd asked for more, we would have paid it."