Deyan Deyanov, 29, who has a mental health condition, faces 15 to 20 years in a psychiatric unit after being found guilty of killing Jennifer Mills-Westley in Los Cristianos in May 2011, the BBC reported.
Prosecutors said Deyanov repeatedly stabbed Mills-Westley, then beheaded her at a store in the Canary Islands resort of Los Cristianos.
In court, Deyanov said "voices" had told him he was "an angel of Jesus Christ who is going to create a new Jerusalem."
It was revealed that Deyanov had been arrested a number of times for violent crimes and spent time at at least two mental health facilities; Glan Clwyd Hospital in North Wales and Tenerife's La Candelaria hospital.
In a statement, Mills-Westley's daughters Sarah and Sam said: "It is clear to us that there has been a catalog of failings; unfortunately it is now left to us to piece these together as we still have so many unanswered questions. We would like to make a plea that the care of people like Deyan Valentinov Deyanov is taken more seriously. He is a young man who has clearly been failed by a number of authorities, in the U.K., Spain and most likely others."