Determination of chronological order of crossed lines of ballpoint pens by hyperspectral image in the visible region and multivariate analysis.

Abstract

Determining the chronological order of crossed lines is a recurrent problem in forensic analysis of documents. One of the most important requirement of these analyses is the use of non-destructive techniques to maintain the integrity of the documents for further analysis as judicial evidences. Thus, this work proposes an objective, non-destructive, easy-to-execute analysis protocol for forensic analysis, using the hyperspectral mode of the VSC6000®, which is an equipment found in most laboratories of questioned documents. Seven blue ballpoint pens of different brands were used to make crossings on white paper, a total of 49. The spectra were obtained from 400 to 1000 nm, and analyzed with HYPER-Tools. Initially, univariate analysis was used, selecting discriminating wavelengths to visualize the images and determine the chronological order of the crossings, and then, when necessary, a multivariate approach using Multivariate Curve Resolution - Alternating Least Squares (MCR-ALS) was applied. The interpretation of the order was made visually, taking into account characteristics of the strokes, such as the continuity and amount of ink. In this way, it was possible to determine the chronological order of 31/49 crossings, which corresponds to an overall rate of 63% accuracy. The method was validated by performing a double-blind test with 8 crossings, which indicated only a small influence of the analyst. The method was also applied to the analysis of a police inquiry, which was provided by the Federal Police and compared with the routine analyzes. The results were concordant but the proposed method provided a more objective analysis than the ones currently in practice at the Police.