Basque Ertzaintza police said they were alerted to the incident by a passer-by who spotted Carlos dragging a prostitute by the hair inside his martial arts gym in Bilbao.
Police found the woman tied up with visible signs of torture and no pulse, online newspaper El Correo reported Monday.
It took 30 minutes to revive the woman, who was then transported to Basurto hospital.
Carlos, 47, was with the woman, hiding in a tiny room, TheLocal.es reported.
Police said they discovered bone remains during a search of the gym, though they aren't sure if they're human remains.