Identifying the author of illegal documents through text mining

Abstract

The eŠectiveness of identifying the author of an illegal document by using text mining was investigated. The suspected writing evaluated in this study was a claim of responsibility written by a 14 year-old boy, which stated that he committed thè`Kobethè`Kobe child murders'' in 1997. It was compared with control writings including confessions, and an essay that we knew were written by the same boy, as well as with irrelevant materials including various essays written byˆvebyˆve junior high school students , and claims of responsibility in four past criminal cases. First, the writings in each document were digitalized and converted to textˆlestextˆles. Then, the relative frequencies of bigram of letters, bigram of part-of-speech taggers, sentence lengths of each document, and rate of using Kanji, Hiragana, and Katakana were calculated. Results of sammon multi-dimensional scaling and hierarchical cluster analysis indicated that the text in the suspected writing was arranged identically or similarly to groups of texts in control materials, where they were arranged diŠerently from groups of texts in irrelevant materials. In a separate analysis, the suspected writing was substituted with a document written by a diŠerent oŠender and we conducted the identical procedure described above. Results demonstrated that texts in the suspected writing were in a diŠerent form control and irrelevant texts. These results indicated the eŠectiveness of identifying an author by using text mining when examining forensic documents.