Non-invasive detection of superimposed latent fingerprints and inter-ridge trace evidence by infrared spectroscopic imaging.

Current latent print and trace evidence collecting technologies are usually invasive and can be destructive to the original deposits. We describe a non-invasive vibrational spectroscopic approach that yields latent fingerprints that are overlaid on top of one another or that may contain trace evidence that needs to be distinguished from the print. Because of the variation in the chemical composition distribution within the fingerprint, we demonstrate that linear unmixing applied to the spectral content of the data can be used to provide images that reveal superimposed fingerprints. In addition, we demonstrate that the chemical composition of the trace evidence located in the region of the print can potentially be identified by its infrared spectrum. Thus, trace evidence found at a crime scene that previously could not be directly related to an individual, now has the potential to be directly related by its presence in the individual-identifying fingerprints.