Overlapping fingerprints are often found at crime scenes, but only individual fingerprints separated from each other are admissible as evidence in court. Fingerprint components differ slightly among individuals, and thus their fluorescence spectra also differ from each other. Therefore, the separation of overlapping fingerprints using the difference of the fluorescence spectrum was performed with a hyperspectral imager. Hyperspectral data (HSD) of overlapping fingerprints were recorded under UV LED excitation. Principal component analysis (PCA) and multivariate curve resolution—alternating least squares (MCR–ALS) were applied to the HSD to determine the optimal method for obtaining high‐contrast images of individual fingerprints. The results suggested that MCR–ALS combined with PCA‐based initialization is capable of separating overlapping fingerprints into individual fingerprints. In this study, a method for separating overlapping fingerprints without initial parameters was proposed.

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In order to detect latent fingerprints that could be damaged by liquid or powder reagents, non‐destructive processes such as gaseous reagents have been developed. In this report, we propose the use of fine mist generated when hot vapor of high‐boiling‐point liquids is rapidly cooled by surrounding air for fingermark detection. Octyl acetate (OA), 2‐phenoxyethanol (2PE), and methyl decanoate (MD) were found to efficiently produce mist when heated to 230°C. By combining these liquids with p‐dimethylaminocinnamaldehyde (DMAC) and cyanoacrylate (CN), our team demonstrated effective fluorescence staining of cyano‐treated fingermarks using DMAC/OA misting or DMAC/2PE misting, and one‐step fluorescence detection of latent fingermarks without cyanoacrylate treatment using DMAC/OA/CN misting or DMAC/MD/CN misting. Fingermark fluorescence was efficiently observed by excitation with a blue LED light (max. wavelength 470 nm) equipped with an interference filter and passing through a 520 nm long‐pass filter. We successfully obtained fluorescent images from fingermarks on several substrate materials using the developed misting method.