From:http://net2.netacc.net/~mafg/jtchick/inquistn.htm
The Spanish Inquisition, and the Inquisition in Venice and other countries, must not be identified with the ecclesiastical Inquisition.They were mixed tribunals, with the civil element predominating, and their excesses cannot be charged to the Church.
The Spanish Inquisition, established in 1481 by Ferdinand and Isabella, was intended primarily for the Mohammedan converts to Catholicism, in the old Arab kingdoms, who were suspected of wishing to return to their old religion, and for disguised Jews, many of whom had succeeded in becoming priests and even bishops. The tribunal, once established, also directed its activity against murder, immorality, smuggling, usury, and other offenses. The king appointed the Grand Inquisitor and the other officials, and also signed the decrees; and the penalties were inflicted in his name. Pope Sixtus IV approved the Spanish Inquisition, because he was under the impression that an ecclesiastical Inquisition was to be established; when the true state of the case was brought to his knowledge, it was too late; all that he and his successors could do was to protest against its excesses. The Spanish kings made extensive use of the powers of the Inquisition against obnoxious prelates and nobles who were not subject to the jurisdiction of other tribunals. On one occasion the Pope had great difficulty in rescuing Cardinal Caranza, Primate of Toledo, from the hands of the Inquisitors.