Hi, Lena - I did a Google search and came up with the site Masato linked to, the one that had many versions of the song. One version was apparently a hymn to the Blessed Mother (Mary). This site has just the hymn, with a MIDI (click) with a wonderful tune in the background. Could it be the tune you're seeking?
Apparently, at least some versions of the song are Sephardic/Ladino. There is an anthology called Folk Songs of Europe that has a listinf for "Prisionero," but I don't know how to get hold of bibliographic information on the book.
-Joe Offer-