Police announced the capture of seven members of a collection "office," who worked on behalf of Colombian drug traffickers, allegedly beating, kidnapping or murdering those who owed the traffickers money, reported El Pais. The arrests followed a 16-month investigation by the Spanish authorities.

The alleged leader of the gang, Luis David Garcia, alias "El Conejo," has previously been linked to a criminal group known as "Los Señores del Acido" (The Lords of Acid) because of their alleged habit of dissolving their victims in acid, reported 20 minutos.

The Señores del Acido were known to have worked closely with the Calle Serna brothers -- Colombian traffickers who were key figures in the Norte del Valle Cartel and its successors the Rastrojos -- a connection that El Conejo is believed to have maintained.

Police arrested the seven gang members on weapons charges, after catching them in possession of an arsenal that included five rifles, two AK-47s, pistols with silencers, two shotguns and an anti-tank grenade launcher. According to the police, the gang intended to transfer the weapons to Mexican traffickers, linked to the Sinaloa Cartel, for use in an attack on their debtors, reported 20 Minutos.

InSight Crime

The Rastrojos' presence in Europe has until now bucked the trend of Colombian organizations ceding trafficking routes to the increasingly powerful Mexican cartels, and the group has retained a significant presence in the European country. However, this may not be the case for long.

Over the last year, the Rastrojos has been in disarray; all its top leaders have been arrested or surrendered, while the remnants of the group have been struggling to combat the advances of rivals the Urabeños in key strategic areas, especially in their heartland in Valle del Cauca province.

From the information provided by the police, it appears El Conejo and his gang had close ties to the Rastrojos, but, with the fracturing of the organization, were looking elsewhere for new contracts -- including Mexican cartels.

This scenario fits the analysis of European police force Europol, which in its 2012 report on drugs and trafficking in Europe, identified Colombian organizations as the only Latin American criminal groups to have a significant presence in Europe beyond simple trafficking connections, but warned of the growing presence of Mexican cartels.