|Year : 2016 | Volume
| Issue : 4 | Page : 203-207
Detecting Latent Prints on Stone and Other Difficult Porous Surfaces via Indanedione/Zinc Chloride and Laser
Shiquan LIU1, Zhongliang MI2, Jian Wu3, Brian Dalrymple4
1 Forensic Science Department, Institute of Evidence Law and Forensic Science, China University of Political Science and Law, Beijing, China
2 Shanghai Police Department, Shanghai Key Laboratory of Criminal Scene Evidence, Shanghai, China
3 Probability and Statistics Department, College of Science, Northeastern University, Shenyang, China
4 Forensic Identification Department, Ontario Provincial Police, Canada
|Date of Web Publication||9-Jan-2017|
Institute of Evidence Law and Forensic Science, China University of Political Science and Law, Beijing
Source of Support: None, Conflict of Interest: None
Lasers and alternate light sources have been recognized as effective tools for latent print detection for over three decades. Luminescence often increases friction ridge contrast to reveal impressions otherwise undetectable. Indanedione/zinc chloride excited by a forensic light source is widely recognized as an effective process for developing latent prints on porous surfaces. This study was designed to evaluate the use of a combination of luminescence excitation and indanedione with zinc chloride to detect latent prints on stones, bricks, and similar difficult porous surfaces. The wavelengths evaluated included 400 nm (violet), 447 nm (blue), 532 nm (green), and 645 nm (red). Latent prints were deposited on a variety of porous surfaces including bricks, cement stones, wood, and cotton fabric, all commonly encountered at crime scenes in China. The surfaces were examined using white light (light-emitting diode flashlight) and laser light sources separately, both before and after treatment with indanedione/zinc chloride. The goal of this study was to evaluate various light sources for their effectiveness in detecting impressions developed by indanedione/zinc chloride on difficult porous surfaces. Results indicated that latent prints on some brick and cement stone surfaces may be effectively detected using 532 nm laser excitation after indanedione/zinc chloride processing.
Keywords: Indanedione, laser, latent print, porous surface
|How to cite this article:|
LIU S, MI Z, Wu J, Dalrymple B. Detecting Latent Prints on Stone and Other Difficult Porous Surfaces via Indanedione/Zinc Chloride and Laser. J Forensic Sci Med 2016;2:203-7
|How to cite this URL:|
LIU S, MI Z, Wu J, Dalrymple B. Detecting Latent Prints on Stone and Other Difficult Porous Surfaces via Indanedione/Zinc Chloride and Laser. J Forensic Sci Med [serial online] 2016 [cited 2023 Jan 28];2:203-7. Available from: https://www.jfsmonline.com/text.asp?2016/2/4/203/197933
| Introduction|| |
Forensic light sources have been instrumental additions to the crime scene and exhibit examination disciplines for decades. Biological evidence detected by luminescence excitation is often the most important evidence in crime scene investigation.
In the 1970s, high-power (4–20 W) and low-power (50–300 mW) argon ion lasers operating in the 488–514.4 nm wavelengths, and copper vapor lasers operating at 510 nm (and sometimes also using the 578 nm wavelength) of the spectrum were widely used. In the 1980s, the advent of efficient dichroic filters able to effectively filter unwanted wavelengths emitted by xenon and indium arc lamps meant the replacement of lasers for most forensic science examinations not requiring fiber optics. Since the 1980s, advances in color light-emitting diode (LED) technology, and a variety of solid-state and semiconductor lasers, have meant a constantly changing array of forensic light source availability.
In the past decade, solid-state and semiconductor lasers with a variety of wavelengths used in forensic examinations have become more popular because of their compact size and weight, as well as their much stronger (than color LED light) output power.
Since 2007, many Chinese crime scene and forensic operations have utilized semiconductor lasers as their forensic light source of choice. Four Lasearcher  semiconductor lasers with purple laser 400 nm, blue laser 447 nm, green laser 532 nm, and red laser 635 nm have been used in this study.
The chemical composition of latent print residue usually includes eccrine gland secretions (amino acids, proteins, polypeptides, salts, etc.) only, but sometimes it may also include a wide variety of contaminates, especially sebaceous matter. Latent print reagents are chemical compounds used for the enhancement of latent impressions through the formation of color, typically in reaction with one or more palmar sweat (eccrine gland) components. Indanedione solution is used as a standard procedure in many laboratories around the world. It produces highly fluorescent latent prints under a variety of development conditions, including ambient room conditions, and hence often may not require further treatment. 1,2-indanedione combined with catalytic amounts of zinc chloride has found widespread operational use for creating optimal friction ridge luminescence (and thus increased contrast) on a variety of porous surfaces.,,,
| Materials and Methods|| |
The laser sources used in this project are as follows:
- Lasearcher model 400, producing 2.2 W at 400 nm, purple laser
- Lasearcher model 400, producing 10 W at 447 nm, blue laser
- Lasearcher model 400, producing 8 W at 532 nm, green laser
- Lasearcher model 400, producing 3.4 W at 635 nm, red laser.
Indanedione working solution
- 1,2-indandione 2500 mg
- Ethyl acetate 225 ml
- Acetic acid 25 ml
- Petroleum ether 40-60 2250 ml
- Zinc chloride stock solution 25 ml.
Latent prints were collected from ten students. Each student put one fingerprint, without any preparation on brick, cement stone, wood, and cotton surfaces. Each student then put another finger, which had been rubbed on their face (to obtain sebaceous matter) on the same surfaces above. It was the second print deposited on the same item.
Chemical processing of latent prints
All the samples were treated with indanedione/zinc chloride in a modified version of the process recommended by Professor Yaping Luo.
| Results and Discussion|| |
Untreated latent prints
Most untreated latent prints, no matter eccrine gland impressions or sebaceous contaminated prints, revealed no ridge detail under white light or laser illumination during the test, however careful observation revealed limited ridge detail on some test surfaces [Figure 1]. Careful photographic procedures were required to capture more detail than what is visible to the naked eye. During our almost 10 years' experience using semiconductor lasers for crime scene and forensic laboratory examinations, we have found that the intensity of inherent latent print fluorescence depends on a variety of factors, including the following:
|Figure 1: The same latent print on the brick surface photographed by: (a) white light-emitting diode; (b) 532 nm photographed through a cutoff filter; (c) 447 nm photographed through a cutoff filter; (d) 400 nm photographed through a cutoff filter. In latent print detected by light-emitting diode, 532 nm and 447 nm, it is hard to see any ridge detail, but 400 nm can find a few ridge details|
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- Smoothness, porosity, texture, color, and other characteristics of the substrate
- Composition (usually unknown) of the latent print matrix deposited by (of lifted away by) the friction ridge skin
- Forensic light source wavelength(s) and power (W/mW)
- Viewing (goggle) and photographic filters (e.g., wide-band cutoff, narrow-band, dichroic)
- Imaging factors such as spatial, spectral, and radiometric (tonal) resolution and sensitivity at various wavelengths.
Even though that only very limited friction ridge detail can be seen before, during and after various examination/processing/illumination steps, it is necessary to record all ridge details for later analysis, including digital image processes sometimes capable of merging fragmentary information into meaningful impressions. [Table 1] shows the amount of visible ridge details of untreated latent prints under green laser of 532 nm, blue laser of 447 nm, purple laser of 400 nm, and red laser of 635 nm illumination.
|Table 1: Untreated latent prints (both eccrine gland and sebaceous gland prints)|
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The same latent print on the brick surface was photographed by: (a) white LED; (b) 532 nm photographed through a cutoff filter; (c) 447 nm photographed through a cutoff filter; and (d) 400 nm photographed through a cutoff filter. In latent print detected by LED, 532 nm and 447 nm, it is hard to see any ridge detail, but 400 nm can find a few ridge details.
Treated latent prints
The latent prints on each test surface were processed with indanedione/zinc chloride and then heated in an oven with 80°C for 10–20 min [Figure 2].
|Figure 2: The above samples were heated in an oven: (a) bricks; (b) cement stone; (c) wood; (d) cotton|
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The purpose of laser illumination is to excite fluorescence (increase contrast) in the ridge detail resulting from treatment with indanedione/zinc chloride. With fluorescence, light is absorbed in one wavelength and re-emitted in a longer wavelength (i.e., Stoke's shift). Appropriate blocking filters are used in anti-laser goggles and in front of camera lenses to block (typically >99%) the laser light and allow higher spectrum color luminescence to pass through and be seen or photographed.
[Figure 3] shows the bricks under 532 nm, 447 nm, and 400 nm light sources. Latent prints treated with indanedione/zinc chloride showed the strongest fluorescence under 532 nm illumination. Those impressions were visible between 3 h and 3 days after processing, and somewhat visible even 30 days later [Figure 3]. However, typically, the best ridge detail was visible on or around the 3rd day during the testing.
|Figure 3: The same latent print on a brick treated with: (a) 532 nm photographed immediately after processing; (b) 3 hours with indanedione at 532 nm; (c) 3 days with indanedione at 532 nm; and (d) 30 days with indanedione at 532nm|
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[Figure 4] shows cement stone under 532 nm, 447 nm, and 400 nm illumination. Latent sebum deposit prints treated with indanedione/zinc chloride showed the strongest fluorescence under 532 nm [Figure 5] and they were visible between 3 h and 30 days after processing [Figure 6].
|Figure 5: The same latent print on cement stone treated with: (a) 532 nm; (b) Indanedione/zinc chloride at 532 nm; (c) indanedione/zinc chloride at 447 nm; and (d) indanedione/zinc chloride at 400 nm|
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|Figure 6: The same latent print on cement stone treated with indanedione/zinc chloride, photographed with 532 nm illumination through a cutoff filter: (a) 3 h after processing; (b) 3 days after processing; (c) 30 days after processing|
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Ten types of wood were used as samples and only four latent sebum deposit prints were detected by indanedione at 532 nm [Figure 7]. The four wood surfaces were photographed by a microscope [Figure 8]. The wood grain structure varied from approximately 5 to 10 µm between ridges. The porous, permeable substrate hindered uniform recording and/or visualization of some friction ridge detail.
|Figure 7: The latent prints on four wooden surfaces: (a) indanedione/zinc chloride, 532 nm; (b) indanedione/zinc chloride, 532 nm; (c) indanedione/zinc chloride, 532 nm; and (d) indanedione/zinc chloride, 532 nm|
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[Figure 9] includes the only two latent sebum deposit prints detected on cotton fabric during the testing. The images were adjusted using Fourier transform image processing to reduce fabric interference and maximize contrast [Figure 10]. As with other difficult surfaces, there is greater contrast in the version photographed with 532 nm illumination. The images were evaluated using PiAnoS software (freely available on http://ips-labs.unil.ch) and deemed suitable for comparison, including more than six discernible minutiae in each impression [Figure 11].
|Figure 10: Fingerprint images adjusted by Fourier transform image processing on cotton fabric surface|
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|Figure 11: Quality assessment by PiAnoS software (freely available on http://ips-labs.unil.ch). Green represents high-quality area; orange represents medium-quality area; and red represents low-quality area|
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| Conclusion|| |
Testing showed that a combination of indanedione/zinc chloride and green wavelength luminescence excitation can effectively detect latent prints on difficult porous surfaces such as bricks, cement stones, wood, and cotton fabrics [Table 2]. Based on the testing, additional research is needed to determine optimal processing factors such as reagent strengths, humidity chamber temperature, and relative humidity.
Among the wavelengths evaluated, 532 nm proved to be most effective for detecting latent prints processed with indanedione/zinc chloride. We believe that future research of this technique holds promise for harvesting additional latent prints on difficult surfaces.
This project was supported by Award number 2016XCWZK09 funded by Shanghai Key Laboratory of Crime Scene Evidence. The opinions, findings, conclusions, and/or recommendations expressed in this publication are those of the authors and do not necessarily reflect those of the authors' employers or professional organizations, including the Shanghai Police Department.
For further information, please contact:
Shiquan LIU, Ph.D. Postdoctoral fellow, Institute of Evidence Law and Forensic Science, China University of Political Science and Law, Beijing 100000, China. E-mail: email@example.com
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]
[Table 1], [Table 2]