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.

CNN: Spain 'al Qaeda cell' may have targeted Gibraltar