ARMED with whistles and dressed in athletic clothing, the vigilantes start their daily round at one of their favourite hunting grounds: Barcelona's Diagonal metro stop, a perfect feast of tourists and commuters.
It takes less than five minutes to spot their first target: "Pickpocket!"
Like a wolf pack, five members of the 10-strong citizens' patrol start chasing the supposed thief, out into the street. He's not alone. "There's another one," they cry.
The pair are dragged back into a corner of the station by security and, with the help of the vigilantes, guarded until police arrive.
By then, tensions have risen considerably. The alleged pickpockets have grown aggressive, threatening patrol members.
Some have taken justice into their own hands. "Who used the pepper spray?" an officer asks. "You do a good job, but sometimes you go too far. If he's left blind, the one who did it will be in trouble."
The pepper-sprayer makes himself known and apologises to the group. Another member is regretful of speaking out of line in front of journalists.
The group leader gently chides them, before they pat each others' backs and laugh. The patrol continues.
The leader, Eliana Guerrero, is a nemesis for pickpockets. For 12 years, she acted as a lone wolf, warning tourists of thieves in the city's metro.
But the increase in crimes such as violent robberies - up 31 per cent from last year - has put security at the top of the public agenda, and others have decided to join her.
According to police, around 100 pickpockets make a daily living in the Barcelona metro. Law enforcement has found a useful ally in the patrols. But Catalan police prefer to distance themselves from the patrols in public.
Last July, the city council threatened the patrols with legal action. But patrol members doubt the council will dare, especially since security has become the main concern for locals.
In four years, residents citing it as their biggest worry have increased from 3.4 per cent to 27.4 per cent.
Police insist they take it seriously - with 300 new officers to be deployed this month. But they say the social alarm is not proportionate to reality.
The Catalan Association of Criminologists also deny any security crisis.
"We're used to very low rates of violent crimes, so whenever it goes up, the increase seems much bigger," says Pedro Campoy, its spokesman. "Crime rates in other European cities receiving millions of tourists a year are higher."
The vigilantes remain committed to their cause. Patrulla Ciudadana, Ms Guerrero's group, spends around three hours every day guarding the subway and some of the busiest tourist spots.
But some are wary that the more people that take part, the more difficult it will be to control them.
Roger Maddocks, born in the Isle of Man but living in Barcelona for eight years, joined Ms Guerrero last April, but later broke with the patrol.
He said: "We can have a list of rules, but you end up having random people who think they're Rambo start pushing thieves to the ground, using pepper spray."
While distancing himself from the patrols, Mr Maddocks still praises their work.
"I'm happy citizens have realised there is a problem," he said. "If that involves a group of people patrolling the metro to make it safer, I'm OK with that. I'm just not going to do it myself."
The Telegraph, London