Juan Jesus Narvaez Goni and Itziar Alberdi Uranga had been fugitives since 1992, ThinkSpain reported. They were arrested in Puerto Vallarta, on the Pacific coast of Mexico, where they had been living at the same address for six years with their two children, authorities said.
Spanish prosecutors say the couple were members of Euskadi Ta Askatasuna -- or Basque Homeland and Freedom -- a group that has been waging an armed struggle for Basque independence since 1959. Narvaez and Alberdi allegedly belonged to the Liberated Ekaitz Commando and were involved in 18 killings in one year, including the assassination of Manuel Broseta, a university dean gunned down in Valencia.
After the couple were arrested Sunday, neighbors in Puerto Vallarta described them as "very polite." Residents of the area said their children have disappeared.
Narvaez and Alberdi were being held in Mexico, awaiting extradition proceedings.