Betrayal or perfidy. According to the Spanish Penal Code: «There is treachery when the guilty commits any of the crimes against the Life, using means, methods or forms in the execution that tend directly and especially to ensure it, without risk for your person that comes from the defense that could make the offended».
Treachery is an aggravating circumstance in crimes against persons. In the murder It is not clear which one aggravating generic, but as a qualifier of saying crime; the same as in the homicide, by her turned into murder.