Development of latent friction ridge prints

Abstract

Apparatus to produce a spatially and temporally uniform heat source is described and this is used to visualize latent fingerprints deposited onto thermal paper by raising the temperature of the paper. Results show an improvement over previous techniques, particularly when fingerprint deposits are aged or the developed fingerprints faint; visualization being enhanced by the use of an LED light source. An investigation of the components in fingerprint sweat likely to affect the solubility and hence colour change of the dye present in the thermal paper has shown that polar protic solvents able to donate a proton are favoured and a polar amino acid found commonly in eccrine fingerprint sweat (lysine) has been shown able to produce the desired colour change. Aged fingerprint deposits on thermal paper from a variety of sources up to four years old have been visualized with this technique.

Claims

1. A method for developing a latent fingerprint deposited onto the surface of a portion thermal paper, the method comprising the steps of: commencing uniform heating of the portion of thermal paper to raise the temperature thereof to a temperature which is below the normal temperature at which the surface layer changes color; monitoring the contrast of a developing fingerprint; and terminating heating when the contrast of the developing fingerprint reaches a desired state or decreases by a pre-determined threshold percentage.

2. A method as claimed in claim 1, in which the step of monitoring the contrast of a developing fingerprint is performed using an array of light detectors.

3. A method as claimed in claim 1, in which the portion of thermal paper is actively cooled after heating is terminated.

4. A method as claimed in claim 1 in which the surface layer of the portion of thermal paper is illuminated during heating.

5. A method as claimed in claim 4, in which the paper is illuminated with ultraviolet, visible light or infrared.

Description

(1) The present invention will now be more particularly described, the way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1(a)—Schematic representation of apparatus used to develop latent fingerprints deposited onto thermal paper;

(3) FIG. 1(b)—Photograph of the apparatus in use;

(4) FIG. 2—Grading of fingerprints developed on thermal paper using the grading scale shown in Table 1;

(5) FIG. 3—Examples of grade 4 developed fingerprints for elapsed times of (a) 1 hr, (b) 1 day, (c) 2 days, (d) 1 week, (e) 2 weeks, (f) 3 weeks and (g) 4 weeks;

(6) FIG. 4—A faint fingerprint developed after 4 weeks elapsed time and photographed with (a) a Daylight™ lamp, (b) a white Crime-Lite and (c) a blue LED;

(7) FIG. 5—A developed mark of (a) lysine solution and (b) distilled water on heated thermal paper;

(8) FIG. 6—Developed fingerprints on (a) a receipt dated 2009 and (b) a receipt dated 2006. Both (a) and (b) were photographed with the blue LED light source;

(9) FIG. 7—a front elevation of a print recovery apparatus formed according to an alternative embodiment;

(10) FIG. 8—a perspective view of the apparatus of FIG. 7 shown with a sample for analysis;

(11) FIG. 9—a perspective view of the apparatus of FIG. 7 and FIG. 8 shown with a lid lifted ready to receive a sample;

(12) FIG. 10—a perspective view of the apparatus of FIG. 9 shown with a sample in position ready for analysis;

(13) FIG. 11—a perspective view of the apparatus of FIG. 10 shown with the lid closed and ready for analysis to commence;

(14) FIG. 12—a photograph of a sample shown following a recovery process in the apparatus of FIGS. 7 to 11;

(15) FIG. 13—a plan view of the underside of the lid of the apparatus of FIGS. 7 to 11;

(16) FIG. 14—a magnified view of a detection cell forming part of a detection array provided by the lid; and

(17) FIG. 15—a graph showing an example of a recovery process performed using the apparatus of FIGS. 7 to 11.

(18) An example of apparatus used to heat latent fingerprint deposits on thermal paper is shown schematically in FIG. 1(a) with FIG. 1(b) showing a photograph of the apparatus in use. In FIG. 1(a), A represents a 1 mm thick brass rectangular plate, placed onto the flat surface of a hotplate (Barlowworld Scientific, Stone, UK). To this, via a brass piano hinge (B), is fixed a 1 mm thick glass rectangular plate (C) of similar dimensions to the brass plate such that the glass plate can be raised or lowered. A sample of thermal paper to be treated (D) is placed onto the brass plate and the glass plate lowered to ensure good thermal contact between the paper and brass. E represents a housing for a series of 395 nm peak wavelength LED lamps (F) (Yoldal, Zhonghe City, Taiwan), used to illuminate the thermal paper. Reasons for selection of this illumination wavelength are discussed later.

(19) Latent fingerprint deposits were taken from 20 male and 20 female donors onto thermal paper (Till Rolls Direct, Bletchingly, UK) such that each person donated impressions from seven different fingers. Fingerprints were deposited by pressing a finger onto the paper surface for 1-2 seconds with a light pressure sufficient to ensure contact between the finger and paper. Whilst no attempt was made to regulate the amount of pressure applied by individuals, this procedure was intended to produce reasonably uniform deposition. No artificial stimulation of sweat was employed such as placing the hand in a plastic bag (14) or wearing a latex glove prior to deposition (15). One of the impressions from each donor was developed using the above apparatus after either 1 hr, 1 day, 2 days or 1, 2, 3 or 4 weeks, this time period being in keeping with that considered by Wakefield and Armitage (12). Between deposition and development, the thermal paper was left in an office environment, exposed to both artificial and natural light, but not direct sunlight. Donors had not washed their hands 20 minutes before deposition and, prior to deposition, each donor rubbed their hands together to ensure a uniform distribution of sweat as previous research has indicated that sweat composition can differ between fingers for the same individual (16).

(20) Fingerprint ridge development on thermal paper after the application of heat as described above was graded based on the quality of ridge detail visible (as a black impression on the white paper). For this, the grading system devised by Bandey (17) was used and this is reproduced in Table 1. Initial experimentation determined that, for fingerprint development, the optimum temperature for the top surface of the brass rectangle was 44° C. This was measured across the top surface of the brass rectangle by means of a k-type thermocouple and found to vary both spatially and temporally by <±0.5° C. This development temperature is in keeping with that reported by Wakefield and Armitage (12) of between 45° C. and 47° C. depending on the brand of thermal paper.

(21) Samples from only two of the 40 donors failed to produce any fingerprint ridge development for any of the time periods listed above. Of the remaining 38 donors, FIG. 2 shows that the majority in all time periods gave a grade 4 on the Bandey scale (full ridge development). Over time, the number of donors that gave a grade 4 diminished from 36 (after an elapsed time before heating of 1 hr) to 19 (after an elapsed time of four weeks). However, the number of donors that gave a grading of 0-2 only increased slightly in this time period from two (after 1 hr) to nine (after four weeks). Therefore, the majority of donors (78%) still produced a grading of 3 or 4 after an elapsed time of four weeks. Development time (t) (i.e. the time that the thermal paper was required to be in contact with the brass rectangle for fingerprint development to occur) varied between individual donors in the range 2 s≦t≦20 s. This development time is less than that reported by Wakefield and Armitage (12) and this may be as a result of the improved thermal contact between the heat source used here (the hotplate and brass rectangle) and the thermal paper. There was no evidence to suggest that t increased with elapsed time before development. FIG. 3 shows typical examples of grade 4 development for each of the elapsed times. All images in FIG. 3 were taken whilst the paper was illuminated with a Daylight® lamp (Daylight Company, London U.K.) although office lighting as illumination gave similar results.

(22) The number of developed fingerprints giving grade 3 or 4 after an elapsed time >2 weeks is in contrast to the results of Wakefield and Armitage (12) where no fingerprint development was observed for an elapsed time >2 weeks. As discussed by Wakefield and Armitage, these differences may be due to the variation in chemicals used in the manufacturing process for different brands of thermal paper. Further, Wakefield and Armitage noted that developed fingerprints had faded one week after development. Here, developed fingerprints did not exhibit any fading for at least 26 weeks after development (the time limit of the experiment). Again, this difference may be due to a variation in the chemicals used in the manufacturing process.

(23) It was noticed that, for elapsed times of greater than two weeks, some of the developed images were faint and difficult to see when the paper was under the glass plate and being heated. As this would affect the heating time required (t), a light source to illuminate the paper whilst being heated was investigated. It was found that blue light produced the most visible contrast between the paper and a faint developing fingerprint and so the housing shown as E in FIG. 1 was constructed to enable the paper to be illuminated and observed whilst being heated. FIG. 4 shows a faint fingerprint developed after four weeks elapsed time, and photographed with (a) a Daylight® lamp, (b) a white Crime-Lite (Foster & Freeman, Evesham U.K.) and (c) a blue LED with 395 nm peak wavelength. Whilst having a somewhat ‘dotty’ appearance, the dots are most distinct when illuminated with the blue LED. It was observed that there was greater transmission of the blue light through the thermal paper compared with both the Daylight® lamp and the white Crime-Lite and this is thought to be contributing to the improved visualization of faint fingerprints.

(24) It was noted above that polar organic solvents initiate colouring of the leuco dye in thermal paper (3). This reaction was investigated further in order to determine the fingerprint sweat components that act as a solvent for the dye and hence are able to reduce the temperature at which it changes colour. Using the same brand of thermal paper as above, various common polar and non-polar solvents were applied to the paper by means of a small brush. The results are shown in Table 2 where it can be seen that, at room temperature and with no additional heating, polar protic solvents (with the exception of water) all increased the solubility of the dye. Thus, for the dye used in this brand of thermal paper, it was assumed that the most favourable solvent would be polar protic, that is, one that can donate a proton attached to (for example) oxygen in a hydroxyl group (OH) or nitrogen in an amino group (NH.sub.2) (18).

(25) It is well known that certain amino acids have a polar side chain, including some that are found commonly in eccrine sweat (18). One such amino acid, lysine (16) has an amino group side-chain that is fully protonated in a weak base solution (18).

(26) To test whether a solution of lysine would increase the solubility of the dye, a concentration of 10 mgL.sup.−1 of lysine was prepared by dissolving the monohydrate (Thermo Fisher Scientific, New Jersey US) in distilled water. This concentration was chosen as it is typical of that found in fingerprint sweat (16). The solution was applied to the thermal paper by means of a small brush. As a control, a similar amount of the distilled water was also applied to the paper. Neither the lysine nor the water gave any colour change to the dye at room temperature. However, on heating using the apparatus described above, a colour change to the dye was noted, which was much more pronounced for lysine than for the water control. The results are shown in FIG. 5 for (a) lysine and (b) water. Thus the amino acid present in eccrine sweat may well be affecting the solubility of the dye observed when heating fingerprint sweat deposits. Fingerprint deposits of eccrine sweat were obtained by asking the same 40 donors to wash their hands in warm soapy water and then to wear a latex glove for 20 minutes before donating fingerprints (14). Results obtained were found to be consistent with those described above.

(27) Samples of used thermal paper, that is, paper that had been used to print receipts etc. were obtained from a variety of sources including automatic teller machines, supermarket checkouts, credit/debit card transactions and supermarket product labels. These samples had been stored since they had been printed and ranged in age from a few days to several years. In total, 50 different receipts were subject to the heat treatment described above. Prints graded 3 or 4 were found on four (8%) of the samples, FIG. 6 showing typical examples from receipts dated 2009 and 2006. In FIG. 6, both developed fingerprints were photographed using the blue LED light source.

(28) By introducing a spatially and temporally uniform heat source, development of fingerprint ridge characteristics deposited as sweat onto thermal paper has been achieved. Results have shown an improvement over previous research, particularly with regard to the visualization of aged or faintly developed fingerprints, by employing a blue LED light source with 395 nm peak wavelength. An investigation of the components in fingerprint sweat that affect the solubility and hence colour change of the dye has shown that polar solvents able to donate a proton are favoured and an amino acid found in eccrine fingerprint sweat (lysine) has been shown to produce the desired colour change. Aged fingerprint deposits on thermal paper from a variety of sources have been visualized with this technique.

(29) Referring now to FIGS. 7 to 15 there is shown a print recovery system for use on thermal paper formed according to an alternative embodiment of the present invention.

(30) The Hot Print System (HPS) general indicated 10 has been designed to recover fingerprint detail from thermal paper. As discussed below the HPS will heat the thermal paper whilst detecting any contrast change in the paper. Once the required contrast change has been achieved, the HPS will rapidly cool the paper, revealing a print.

(31) Referring first to FIGS. 7 to 11 there is shown a print recovery apparatus generally indicated 10. The apparatus 10 comprises a base 15 and a lid 20 hinged to the base. The base 15 comprises a glass sheet 16 forming a flatbed surface for receiving a sample as shown best in FIG. 10). Under the sheet 16 is an array of Peltier devices (not shown) which can selectively heat or cool a sample through the sheet.

(32) Referring now also to FIGS. 13 and 14, the lid 20 carries a frame 21, which in turn carries a printed circuit board which serves as an emission/detection array module 30. The frame 21 is mounted in the lid such that it can move to accommodate variations in the thickness of a sample.

(33) The module 30 includes a plurality of LED's 32 and a plurality of photosites 34 arranged in generally square patterns. A plurality of microprocessor units 36 are also provided and linked to respective sub-arrays of emitters and photo sites.

(34) Referring now also to the graph of FIG. 15, in use, a sample 50 is presented (FIG. 8) and the lid 20 is lifted (FIG. 9) to allow the sample to be laid onto the bed 16 (FIG. 10). In this embodiment the user is instructed to lay the sample with any writing facing upwards as shown. This is stage I on FIG. 15.

(35) Subsequently the lid is closed and a start button 17 on the base is pressed. In a first stage the photosites each take an average reading and discount any that it believes are seeing only the black plate. The system then begins to heat up the sample 50 uniformly.

(36) The photosites read and average the light they receive during the whole heating process. As a result latent prints will start to be developed and this translates into a different level of brightness which can be interpreted as contrast by the photosite array; this is stage II on FIG. 15.

(37) When the value of light received from any one cell reduces beyond a set threshold percentage, scaled to each photosite, this is indicative of the appearance of a print and the heating process will be terminated to prevent further heating of the sample; this is stage III on FIG. 15.

(38) The Peltiers are then be reversed to cool for 30 seconds and then the Peltiers continue to cool for a further 20 seconds. The Peltiers then turn off. The fan continues to work for 90 seconds, after which the process can be repeated (with the same or a different sample). The cooling step therefore protects the sample from overdevelopment; this is stage 1V on FIG. 17.

(39) The sample 50 can now be removed from the device 10 with the developed print 55, as shown in FIG. 12.

(40) There now follows a description of an apparatus forming an embodiment of the present invention. For the avoidance of doubt, all of the following features should be regarded as optional and may be used together or separately.

(41) Power Supply

(42) The internal power supply is an SP320-24 capable of operating from a standard domestic supply of between 90 v and 264V AC, 47-63 Hz.

(43) The internal power supply is capable of operating from a 12 v vehicle supply.

(44) The maximum power consumption is approximately 30 W.

(45) The unit is inherently safe.

(46) It is not be possible for the user to come into contact inadvertently with any electrical or mechanical elements inside.

(47) The HPS has an automatic shutdown should a defined time out be exceeded.

(48) There is a power switch, which will immediately cut all power to the unit.

(49) The unit has a safety warning sticker on it.

(50) When supplied to a user, the unit has a band around the packages which instructs the customer to read the instruction manual before use.

(51) The unit has a 250V 2 AMP fuse incorporated in to the IEC socket

(52) Internal Mechanism

(53) The product is cooled by two 12 v fans.

(54) The product has four different IEC connector plugs for the four different likely sockets (UK, Europe, US and Australasia).

(55) The product has a power lead capable of operating from a 12 v vehicle supply.

(56) The product has an internal power supply to allow main connection from 110-240 v.

(57) The heat source is eight Peltiers.

(58) The Peltiers are mounted between two plates; the top plate is 0.5 mm aluminium and the bottom plate is a 3 mm aluminium heat sink.

(59) The Peltiers are adhered to the plates with thermally conductive double sided tape.

(60) The top plate is anodised.

(61) The bottom heat sink is anodised.

(62) The Peltier wiring comes out of the side of the Peltier heat plate.

(63) The heat plate is mounted to the underside of the main housing.

(64) The product has a door open switch comprising of a reed switch and a magnet.

(65) The cover supports the door open switch.

(66) The lid supports the magnet.

(67) The product has a 24V internal power supply.

(68) The power supply is mounted upside down using four brackets.

(69) The main PCB is mounted on top of the upside down power supply with 3 mm spacers.

(70) The Mosfet power transistors from the main board are mounted to a heat sink which in turn will be mounted to the power supply.

(71) The product has a photosite board to detect the contrast change in thermal paper when heated.

(72) Clips are used to hold the fan wires in place.

(73) The PVC glass holder is sprung inside the lid.

(74) The lid has four inserts to hold the PVC glass holder.

(75) The photosite PCB is attached to the PVC glass holder.

(76) The photosite PCB shall not be warped or twisted.

(77) The glass is flat and 2 mm thick.

(78) The glass is bonded to a stainless steel frame using a jig and double-sided adhesive.

(79) The stainless steel frame is bonded to a PVC holder using a double sided adhesive.

(80) There are two brass blocks inside the lid to add extra weight.

(81) Housing

(82) Base Plate

(83) The product will have an aluminium base plate which is 1.6 mm thick.

(84) Fan holes match the power supply.

(85) The base plate has two angled fan holes.

(86) The fans have finger guard as an integral part of the base.

(87) Foam fin air deflectors will be used around the fans.

(88) The base plate is mounted on five rubber feet.

(89) The base plate has a Grain Finish (240 Grit).

(90) Main Housing

(91) The main housing is of solid construction.

(92) The main housing is polycarbonate which is screwed on to the base plate.

(93) The main housing has a partition between the Peltier heated section and the power supply section. This has a single hole drilled to route the Peltier wiring and a slot to route the fan wires, door switch wire and ribbon cables.

(94) The main housing has a second partition between the Peltier heated section and the front panel section which will have a cut out to house the ribbon cables.

(95) The main housing has M4 inserts moulded in.

(96) The main housing cover houses a reed switch.

(97) The main housing houses an IEC socket to the right rear.

(98) The wiring is routed in a tidy manner to the right rear of the main housing when viewed from the top.

(99) Lid

(100) The product has a plastic polycarbonate lid which will be hinged to the cover.

(101) The lid has a PVC glass holder.

(102) The PVC glass holder houses a stainless steel frame.

(103) The stainless steel frame houses 2 mm thick glass.

(104) The lid has M3 inserts moulded in to fix the inner frame and M2.5 inserts moulded in to fix the PVC glass holder in place.

(105) The lid has a black anodised aluminium frame to hold the PVC frame.

(106) The lid houses a magnet for the door switch.

(107) Front Panel

(108) The front panel PCB is mounted to the main housing.

(109) The main housing has 2 mm spacers to mount the front panel PCB.

(110) The main housing supports the front panel graphic.

(111) The front panel graphic is mounted with double sided adhesive to the cover.

(112) The front panel graphic sandwiches the acrylic light guide to the cover.

(113) The front panel graphic sandwiches the switch piston to the cover.

(114) Electronics

(115) Power Supply

(116) The product has a 24 v internal power supply.

(117) The power supply connects to mains power from 110-240 v.

(118) The power supply connects to mains power using an IEC lead into an IEC connector.

(119) The IEC connector is fitted with 250 v 2 AMP 20 mm fuses.

(120) The power supply is earthed to the base plate.

(121) The unit is able to facilitate an IEC filter if needed and will use flag terminals in that case.

(122) If no filter is used, standard ¼″ blade terminals can be used.

(123) The IEC is connected to the power supply with 1 off 200 mm lengths each of wire, brown, blue and yellow/green.

(124) The power supply connects from the positive and negative terminals to PL10 on the main PCB using 2 red/black figure of eight cables 250 mm in length.

(125) Main Printed Circuit Board (PCB)

(126) The main PCB is mounted on top of the upside down power supply with 3 mm spacers.

(127) The Mosfet powers transistors from the main PCB are mounted to a heat sink which is mounted to the power supply.

(128) Photosite PCB

(129) The photosite PCB detects the contrast change in thermal paper when heated.

(130) The photosite PCB has yellow LEDs.

(131) The photosite PCB has photodiodes.

(132) The photosite PCB has a separate cell which scales the photodiodes individually for factory calibration.

(133) The photosite PCB is mounted to the PVC glass holder 16 mm away from the glass.

(134) The photosite PCB will not be warped or twisted.

(135) The photosite PCB has a black solder resist.

(136) The photosite PCB is connected to SK2 on the main PCB using a 200 mm flat flex cable routed through the lid.

(137) Front Panel PCB

(138) The product has a front panel with a single operation icon, push button and power light to show the status, as per the following:

(139) Power Icon:

(140) Green for on Red for error
Heating Icon: Green for ready Amber flashing for when machine in process (Peltier heat and cool) Amber steady for when pettier cooling process is complete along with a two beeps Green when the system has cooled Red flashing if there is a problem
Push Button: White and constantly on (even during standby)

(141) There will be 1 long error beep if the cycle has timed out.

(142) The front panel is powered by the main PCB.

(143) The front panel is connected to PL2 on the main PCB using a 500 mm ribbon cable

(144) The front panel ribbon cable is routed from the front panel round to the right rear as viewed from the top and through both partitions

(145) Peltiers

(146) There are eight peltiers in series in two strings of four.

(147) The Peltiers are linked by closed end crimps.

(148) The Peltier plate connects to PL8 on the main PCB using 2 red/black figure of eight cables.

(149) Fans

(150) The product is cooled by two 12 v fans.

(151) The fans are connected to PL5 and PL6 on the main PCB.

(152) Door Switch

(153) The door switch will be a reed switch and magnet.

(154) The door switch will be connected to PL1 on the main PCB.

(155) Software/Firmware

(156) Factory Calibration

(157) 1. The system will have a known white material placed under all photosites. 2. The photosites will be turned on and the LED current increased until the photosite with the highest averaged reading approaches the maximum signal (30,xxx). 3. The average reading will be the average of approximately sixteen readings, but more or less as required to achieve stable measurements. 4. At this point the system will record the average readings from each of the photosites and the PWM value for the LED drive current. This will be the level used for normal operation. 5. Each photosite reading recorded at the calibration will be used to scale subsequent photosite readings. 6. The white sheet will be removed to allow a view of the black plate. 7. The photosites will then look at the plate under the known illumination and capture each photosites average reading of the black plate. 8. This is now calibrated as the machine knows what white and black looks like.
User Process 1. The user inserts the sample and presses the button. 2. The fans will start at hex value 0xFF and will operate any time the Peltiers are working. 3. The photosites each take an average reading and discount any that it believes are seeing only the black plate. 4. The system will heat at hex value 0xB5 until the photosites sense a change. 5. The photosites will continue to be read and averaged during the whole heating process. 6. When the value from any one cell reduces beyond a set threshold percentage, scaled to each photosite (to be specified through testing), the heating process will be terminated. 7. The Peltier will then be reversed at hex value 0xFF to cool for 30 seconds. 8. After 30 seconds the Peltier will continue to cool at hex value 0x29 for 20 seconds. 9. The Peltiers will now turn off. 10. The fan will continue to work for 90 seconds. 11. After 90 seconds the process can be repeated.
Functionality

(158) The HPS has the following functions: 1. The machine is plugged in to the mains and the power switch light is off. 2. The power button is turned on, the power switch illuminates and the machine goes to its ready state illuminating the green power light, button light and green icon lights on the front panel. 3. The user will lift the lid, insert the paper, lower the lid and press the button to start the process. 4. The icon light will turn flashing amber to show it is in progress. 5. The system will heat and sense IAW firmware. 6. Once the system has sensed the change, there will be a single audible signal and the heating icon will show steady amber. The user will then open the door to remove the sample. 7. Once the system has cooled to a safe temperature (IAW firmware) the icon will turn green (back to function 4). 8. If there is a critical error in the process the icon flashes red. 9. If the button is pressed with the door open there will be an error sound and process won't start. 10. Instructions

(159) The customer needs to be guided to: Only process thermal paper Put the paper in writing side up Only put thermal paper in the machine (no thick objects) Use only plastic tweezers Understand that the unit is hot Not lift the lid during processing Understand to only push the button in standby state or when the icon is green Only place the system on an flat well ventilated surface A defined cleaning regime
Calibration

(160) The unit self-calibrates every time it is powered.

(161) The customer will have a means of reliably testing the calibration of the machine.

(162) Portability

(163) The HPS is intended to be primarily used on a laboratory bench.

(164) The HPS can also be used in a vehicle.

(165) The HPS may have a reusable carry case to allow safe transport, for example when calibration/repair is due.

(166) Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiments shown and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCES

(167) 1. http://ezinearticles.com/?The-Uses-and-Hazards-of-Thermal-Paper&id=4141727 2. Bowman V, editor. Manual of fingerprint development techniques. 2.sup.nd rev. ed. Sandridge, UK: Police Scientific Development Branch, Home Office, 2004. 3. http://www.bvda.com/EN/prdctinf/en_thermanin.html. 4. Broniek B, Knaap W. Latent fingerprint development on thermal paper using muriatic (hydrochloric) acid. J Forensic Ident 2002; 52:427-32. 5. Schwarz L, Frerichs I. Advanced solvent-free application of ninhydrin for detection of latent fingerprints on thermal paper and other surfaces. J Forensic Sci 2002; 47:1274-7. 6. Sears V. Latent fingerprint development on thermal paper using muriatic (hydrochloric) acid. J Forensic Ident 2002; 52:678. 7. Ma R. Chemical fuming: a practical method for fingerprint development on thermal paper. J Forensic Ident 2006; 56:364-73. 8. Takatsu M, Kageyama H, Hirata K, Akashi S, Yoko Ta T et al. Development of a new method to detect latent fingerprints on thermal paper with o-alkyl derivative of ninhydrin. Rep Nat Res Inst Police Sci 1991; 44:1-6. 9. Schwarz L, Klenke I. Enhancement of ninhydrin or DFO treated latent fingerprints on thermal paper. J Forensic Sci 2007; 52:649-55. 10. Schwarz L, Klenke I. Improvement in latent fingerprint detection on thermal paper using a one-step ninhydrin treatment with polyvinylpyrrolidones (PVP). J Forensic Sci 2010; 55:1076-9. 11. http://www.clpex.com/Articles/TheDetail/1-99/TheDetail97.htm. 12. Wakefield M, Armitage S. The development of latent fingerprints on thermal paper using a novel, solvent-free method. J Forensic Ident 2005; 55:202-13. 13. Scott M. Improved results in the development of latent fingerprints on thermal paper. J Forensic Ident 2008; 58:424-8. 14. Migron Y, Hocherman G, Springer E, Almog J, Mandler D. Visualization of sebaceous fingerprints on fired cartridge cases: A laboratory study. J Forensic Sci 1998; 43:543-548. 15. Worley C G, Wiltshire S S, Miller T C, Havrilla G J, Majidi V. Detection of visible and latent fingerprints using micro-x-ray fluorescence elemental imaging. J Forensic Sci 2006; 51:57-63. 16. Ramotowski R S. Composition of latent finger print residue. In: Lee H C, Gaensslen R E, editors. Advances in fingerprint technology. New York: Elsevier, 2001; 63-104. 17. Bandey H L. Fingerprint development and imaging newsletter: The powders process, study 1. Sandridge: Police Scientific Development Branch, Home Office; 2004 Report No.:54/04. 18. Clayden J, Greeves N, Warren S, Wothers P. Organic Chemistry. Oxford: Oxford University Press; 2001.

(168) TABLE-US-00001 TABLE 1 Grading system for determining the quality of ridge detail for enhanced fingerprints devised by Bandey (17). Grade Comments 0 No development 1 No continuous ridges. All discontinuous or dotty. 2 One third of mark continuous ridges. (Rest no development, dotty). 3 Two thirds of mark continuous ridges. (Rest no development, dotty). 4 Full development. Whole mark continuous ridges.

(169) TABLE-US-00002 TABLE 2 Effect of various solvents on the solubility of the dye in thermal paper at room temperature. Solvent Paper changed colour? Solvent category Acetic acid Yes Polar protic Dichloromethane No Polar aprotic Ethanol Yes Polar protic Ethyl acetate No Polar aprotic Isopropyl alcohol Yes Polar protic Methanol Yes Polar protic Toluene No Non-polar Water No Polar protic