The aim of the paper is to study a philological value of documents that were never intended to serve to such purposes. In this case these are criminological studies and internal documents of Spanish Police and Civil Guard that belong to the lexicographic genre (vocabularies and wordlists). The hypothesis is that as they were never meant to be sold at the book market but were rather intended to be used for the education of policemen and members of Civil Guards in their daily work in the streets of Spanish towns and in the country, it sounds probable that they could reflect rather well the real usage and vitality of Romani loanwords in the Spanish criminal jargon in their times (19th and 20th centuries).