This article suggests the usefulness of the concept of ‘idiolectal style’ in forensic text comparison and presents evidence that was used by the defence in a forensic authorship attribution case to show that the author of four non-disputed faxes could also be the author of four disputed emails, both sets written in Spanish. Apart from qualitative textual analysis, two different quantitative approaches were undertaken: a) the use of the concepts of markedness and saliency in order to establish the rarity in the frequency and use of two grammatical variables - by comparing their behaviour to the one observed in a general corpus - indicated in both data sets the favourite use of two variants - redundant yo and compound periphrastic relative pronoun el cual, and b) the statistical analysis of sequences of linguistic categories classified and grouped the texts in the two sets under analysis (and also a control text set from another real forensic case) very closely, showing their discriminatory potential, in particular when the sequences were bigrams, something which would lead to the conclusion that these two text sets were produced by the same author.