Shooting distance estimation based on gunshot residues analyzed by XRD and multivariate analysis

Abstract

The most used and validated methods for estimating the shooting distance using the gunshot residues (GSR) inforensic labs are based on chemographic colour tests. In these techniques, the cloth-trapped residues are trans-ferred to a surface to be revealed using chemical reagents. However, because they imply a visual inspection, theirinterpretation may vary, thus adding possible errors to the forensic results. Therefore, it is important tofind anobjective analysis technique for deciding during the results interpretation. In this study, X-Ray diffraction (XRD)was used to measure the GSR on cotton-polyester fabrics. The resulting diffractograms were aligned using acorrelation optimized warping (COW) function, and then analysed using partial least squares to latent structures(PLS), and orthogonal PLS (OPLS). Both methods gave good prediction models in the 5&-300 cm distance range,with determination coefficients of 0.99. Using the gun utilized during the shooting rendered good predictionmodels with quite small prediction errors (about 3 and 7%). Combining the two guns for the calculations, resultedin a prediction model with a larger prediction error (about 14%) but still good for predicting the shooting dis-tance. This would indicate that it is possible to use a similar gun to perform a shooting distance prediction withouthaving the actual gun used during the investigated shooting.