The U.S. weapons arm the cartels' military wings and enforcers, such as the Juarez Cartel's enforcement arm, La Linea, or The Line, court documents say.

CNN: On the border: Guns, drugs -- and a betrayal of trust

Reinares said Spanish security services have established that both Chechens received motor-paragliding lessons near La Linea and may have had some instruction before arriving in Spain.

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The authorities said Acosta, who is also known as "El Diego, " admitted that he had directed or participated in more than 1, 500 murders since 2008, when he became the leader of La Linea -- the enforcement arm of the Juarez cartel -- and a local boss for the cartel in the Mexican cities of Juarez and Chihuahua.

CNN: STORY HIGHLIGHTS