The vigilantes collared the short, pot-bellied man at Cajamarca's teeming outdoor market and marched him to their storefront. He was a serial pickpocket, they said.

The man, 42, was made to empty his pockets, shed his shoes, drop to the floor and do pushups. A look of terror etched his face well before the whip stung his backside. He shrieked, jumped to his feet and begged for mercy, claiming he was innocent.

The assembled men and women, all wearing citizen patrol vests and wielding whips fashioned from the twisted sinew of bull penises, didn't believe him. A dozen lashes later, he confessed, and paid $60 to a woman whose cellphone he'd stolen. He got a shower, and was let go.

"That's how we deal with this kind of thief," said the citizen patrol's leader, Fernando Chuquilin, who personally landed the last lash.

For all but the most serious crimes, this is how justice is routinely administered in this highlands provincial capital of 200,000 people: Swiftly, harshly and painfully. And not by the state.

Instead, in response to an eroding criminal justice system, self-appointed bands of vigilantes have taken on the work of police, prosecutors and judges. The rise of these citizen enforcers, who enjoy widespread support in Cajamarca, is just one response in Latin America to the failure of police forces to offer the most basic protections.

"If the police did their jobs there would be no need for us," says Chuquilin.

Peru's 112,000-officer police force is slightly larger than the Latin America norm per capita, but police spend nearly half their time supplementing monthly salaries that average $650 by moonlighting as private security guards.

Peruvian media carry a steady diet of news about cops running drugs and aiding criminal bands. In an opinion poll last year, Peruvians listed the National Police only slightly behind Congress in a ranking of the country's most corrupt institutions. The judiciary came in third.

Still, the periodic whip-cracking raids on brothels that have gained Chuquilin and his cohort national exposure have elicited outrage from human rights activists and gasps from Lima TV reporters, who tend to portray the bands as over-the-top, Andean-style Taliban morality police.

Locally, though, few people complain, including police commanders, judges and prosecutors who acknowledge Chuquilin's popularity and don't interfere.

A big man with an easy smile and an incessantly ringing cellphone, Chuquilin, is the most popular leader among the 30-odd grass-roots citizen patrol units in Cajamarca known as "rondas urbanas," or urban patrols.

People daily visit his no-frills storefront and fill out summonses. No case is too small, no dispute too trivial for this self-anointed judge. The accused don't dare ignore the summonses, and the hearings are often standing-room-only.

He maximizes public exposure by uploading to YouTube videos his group takes of its public lashings.

Chuquilin, 50, also arbitrates cases that authorities consider minor, settling property and debt disputes, family quarrels and marital infidelities. (Adulterous spouses typically get a lashing and an order to be faithful).

If a felony is committed, the rondas turn the transgressor over to police. The harshest sentence they administer, they say, is banishment.

Esperanza Leon, the local chief prosecutor, said the rondas, which are illegal, are trying to create a parallel justice system.

"If this is allowed to spread, there's going to be chaos," she said.

Nevertheless, Leon is often compelled to coordinate with Chuquilin. Recently, the ronderos broke up an auto parts theft ring that Chuquilin claims police wouldn't touch, turning over suspects and evidence to Leon's office.

But his routine wielding of the whip, which he calls "a necessary evil," may be working against him.

Late last year, Dr. Oscar Malpartida, 26, was in Cutervo, a Cajamarca state city of about 50,000, enjoying a night off from his community service work in a nearby village.

He was with his girlfriend and a group of doctors and nurses at a discotheque when about 50 ronderos hauled them outside at 11 p.m., he said. Apparently, they'd decided the party was over.

When he resisted showing them his national ID card, Malpartida said, he was punched in the face. His glasses were broken.

"I committed no crime," he said. "I wasn't making any kind of trouble."

The group was marched to the central square, where the doctors were made to bend over a bench. Each got three to five lashes.

Malpartida refused to submit "and they hit me about 10 times, with whips and sticks." He posted pictures of the welt on his back to Facebook, filed a criminal complaint and left town fast.

Nothing came of the complaint. "These rondas have a lot of power," he said, "It's very difficult to find a prosecutor who will confront them."

Chuquilin said he couldn't answer for the actions of other ronderos. He says 110 criminal complaints have been filed against him alleging assault, kidnapping and other violations.

He has not been prosecuted. But police arrested four other Cajamarca ronderos on charges of resisting authority last month after they blocked the entrance to a discotheque that Chuquilin claims was unlicensed and attracting minors. A prosecutor is investigating possible criminal charges.

In raids of brothels, ski-masked vigilantes under his command have left welts on women they've whipped — and set fire to mattresses and other furniture they carry out into the street.

Prostitution is legal in Peru, but Chuquilin says he only targets bordellos when neighbors complain they are illegally exploiting minors — or are magnets for criminals who rob people nearby. One brothel owner is seeking criminal charges against him.

In a recent raid, in the town of Chota, Chuquilin said ronderos found two under-aged prostitutes. Video they shot shows him compelling the young women to sing Peru's national anthem, then whip one another.

Cajamarca state's chief judge, Fernando Bazan, generally endorses the rondas urbanas.

"People turn to the rondas because they are more accessible," he said. "People rely on them daily — and daily tell us to our face that we are incapable of guaranteeing security."

Bazan sits on an intercultural justice committee that interacts regularly with the city's 800-member rondas as well as the rural peasant patrols, or "rondas campesinas," of which they are an outgrowth.

The first 'rondas campesinas' formed in the 1970s as small farmers united to fend off cattle rustlers amid a dearth of state authority. They won legal status in the 1993 constitution and keep order in scores of rural communities.

Similar systems exist elsewhere in Latin America, particularly in Guatemala and Bolivia where there is a strong indigenous presence.

Their moral authority derives from the close-knit nature of the communities they serve and their power to publicly shame people who engage in anti-social behavior, says John Gitlitz, a sociologist at State University of New York at Purchase.

"You have to get up and publicly beg for forgiveness. And you have to sign a contract promising to behave. And it's always understood that your family will play a big role in guaranteeing that you do so," he said.

In Cajamarca, the rural ronda morphed into an urban variety, so strong that it is the only one in Peru where the vigilantes help police with security for big soccer matches.

Tito Paucar, who sells pirated DVDs at a downtown market stall, is a believer. He was recently robbed at knifepoint, but got no help from the police.

So Paucar, 30, turned to the ronderos. They asked for a physical description and found his assailant the next day, said Paucar, who identified the suspect.

"They started to go through his pants pockets and they found my wallet," he said. "They gave him about five good whacks. I'm very grateful."

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Frank Bajak on Twitter: http://twitter.com/fbajak