Abstract
Latent fingerprint images visualized with ninhydrin can be enhanced by treatment with indium chloride (InCl3) followed by blue-green light excitation of formed fluorescent Ruhemann's Purple (RP)-InCl3 complex. The RP-InCl3 complex showed stronger fluorescence than the well-known RP-zinc complex.
A Crime Scope filtered lamp, an Ar-laser (6 W), a CW green laser (532 nm, 5 W and 10 W) and a pulsed green laser (532 nm, pulse width: 10 ns, pulse repetition rate: 20 kHz , average power: 1 W) were evaluated as light sources for excitation of the fluorescent RP-InCl3 complex, and the pulsed green laser gave the strongest fluorescence on latent fingerprint detection.
By using this ninhydrin-InCl3-pulsed green laser method, latent fingerprints on some kinds of colored paper, the black- printed part of newspaper and the black-toner-printed part of photocopied paper were well-detected with enough fluorescence utilizing an adequate liquid nitrogen temperature. The pulsed green laser was also suitable for a light source for excitation under liquid nitrogen cooling, since it gave very little rise in temperature on the surface of the sample paper.
On the basis of these results, a fluorescence detection system comprised of pulsed green laser, CCD camera, sample chiller and computer has been constructed.
