Basque Ertzaintza police arrested Aguilar Sunday after they were alerted by a passer-by who spotted him dragging a prostitute by the hair inside his martial arts gym in Bilbao.
Police found the woman, whose name was not reported, tied up with visible signs of torture and no pulse. She was revived and transported to Basurto hospital, officials said
Police discovered human bone remains during a search of the gym, TheLocal.es reported.
While in custody, Aguilar said he killed a woman last week under similar circumstances to the abuse of the prostitute Sunday.
Police are searching the Basque capital's estuary after Aguilar said he dropped some of the woman's remains in the bay, the news website said.
Aguilar suffered from a brain tumor for the past two years. He has a police record, though nothing in it indicated a tendency towards violence, TheLocal.es said.