The men had a WhatsApp group named "La Manada," or "The Animal Pack," and are currently serving 15-year sentences handed down by the Supreme Court for raping an 18-year-old woman during Pamplona's San Fermin festival in 2016.
The case earned renown because lower courts convicted them of lesser crimes.
Prosecutors allege the men sexually abused a 21-year-old woman in Cordoba the same year as the Pamplona case, after driving her home from a night club and when she was unconscious. Prosecutors say the men made a video of the assault.
The men pleaded not guilty Monday and exercised their right not to testify.
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