Barcelona Metro passengers were alerted by Eliana Guerrero, a native Colombian who has made it her mission to warn the city against the dangers of pickpockets.
When Guerrero spotted how a French tourist had been pickpocketed and hurt by four thieves as they tried to get away, she blew her whistle to alert bystanders of the incident.
Around 20 passengers waiting on the platform realized what was happening and formed a human barricade to stop the thieves from escaping.
“It's the first time I've seen something like that, it was very exciting,” Guerrero told Spanish daily 20minutos.
Police and security guards were quick on the scene and arrested the felons.
“They're regulars in Barcelona's underground,” police sources told 20minutos.
“Between the four of them they have 501 felonies to their name.”
Guerrero is one many residents in Catalonia's capital who have grown tired of the city's pickpocketing problem in recent years and decided to take matters into their own hands by becoming cazacarteristas, or pickpocket busters.