Very, very briefly, the blame would be on a paranoid king fearful of his throne. There is sooooo much history about this that is never ever mentioned in most texts..but if you are afraid of christians, especially catholics dz I can see grasping at straws.

In 1483 Ferdinand appointed Tomas de Torquemada as inquistor-general for most of Spain. It was Torquemada’s job to establish rules of evidence and procedure for the Inquisition as well as to set up branches in major cities. Sixtus confirmed the appointment, hoping that it would bring some order to the situation.

Unfortunately, the problem only snowballed. This was a direct result of the methods employed by the early Spanish Inquisition, which strayed significantly from Church standards. When the inquisitors arrived in a particular area, they would announce an Edict of Grace. This was a 30-day period in which secret Jews could voluntarily come forward, confess their sin, and do penance. This was also a time for others with information about Christians practicing Judaism in secret to make it known to the tribunal. Those found guilty after the 30 days elapsed could be burned at the stake.