Analysis of water-soluble paper for forensic discrimination.

Water-soluble paper (WSP), which easily dissolves in water, has been found in criminal gang hideouts as evidence in crimes including bank transfer fraud, phone fraud, and grandparent scams, i.e. identity fraud to steal money. Distinguishing WSP products used in crimes is required in forensic investigations to link fraud groups with paper evidence or prove connections among fraud groups. In this work, we investigate distinguishing WSP products. White sheets of six WSP products available in Japan were analyzed by measuring the grammage and thickness, determining additive compounds by X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM)/energy dispersive X-ray spectrometry (EDX), and performing fiber analysis by transmitted light microscopy. The six products were categorized into three groups by grammage and thickness. XRD, XRF, and SEM/EDX analysis provided elemental information about additive compounds and their distribution on the surface. Pulp analysis by Graff "C" stain provided the composition and morphology of the pulp. The six products could be distinguished in a similar way to plain paper by these analyses. Our results demonstrate that conventional analytical methods used for plain paper analysis can also be used to discriminate WSP in forensic investigations.