Recovering obliterated engraved marks on aluminium surfaces by etching technique

A study has been made of the characteristics of restoration of obliterated engraved marks on aluminium surfaces by etching technique. By etching different reagents on 0.61mm thick sheets of aluminium (99wt%) on which some engraved marks had been erased to different depths it was found that the reagent 60% hydrochloric acid and 40% sodium hydroxide on alternate swabbing on the surfaces was found to be the most sensitive one for these metal surfaces. This reagent was able to restore marks in the above plates erased down to 0.04mm below the bottom of the engraving. The marks also presented excellent contrast with the background. This reagent was further experimented with similar aluminium surfaces, but of relatively greater thickness of 1.5mm. It was noticed that the recovery depth increased slightly to 0.06mm; this suggested the dependence of recovery depth on the thickness of the sheet metal. Further, the depth of restoration decreased in cases where the original number was erased and over which a new number was engraved; the latter results are similar to those of steel surfaces reported earlier [M.A.M. Zaili, R. Kuppuswamy, H. Harun, Restoration of engraved marks on steel surfaces by etching technique, Forensic Sci. Int. 171 (2007) 27-32].     

On the sensitivity of some common metallographic reagents to restoring obliterated marks on medium carbon (0.31% C) steel surfaces

Chemical etching, which is the most sensitive method to recover obliterated serial numbers on metal surfaces, has been practised quite successfully in forensic science laboratories all over the world. A large number of etchants suitable for particular metal surfaces based on empirical studies is available in the literature. This article reviews the sensitivity and efficacy of some popular etchants for recovering obliterated marks on medium carbon steel (0.31% C with ferrite–pearlite microstructure) used in automobile parts. The experiments involved engraving these carbon steel plates with some alphanumeric characters using a computer controlled machine “Gravograph” and erasing them to several depths below the bottom of their engraving depth. Seven metallographic reagents of which most of them were copper containing compounds were chosen for etching. The erased plates were etched with every one of these etchants using swabbing method. The results have revealed that Fry’s reagent comprising cupric chloride 90 g, hydrochloric acid 120 mL and water 100 mL provided the necessary contrast and was concluded to be the most sensitive. The same reagent was recommended by earlier workers for revealing strain lines in steel surfaces. Earlier, another reagent containing 5 g copper sulphate, 60 mL water, 30 mL (conc.) ammonium hydroxide, and 60 mL (conc.) hydrochloric acid was proved to be more sensitive to restore erased marks on low carbon steel (0.1% C with ferrite–pearlite structure) [M.A.M. Zaili, R. Kuppuswamy, H. Harun, Restoration of engraved marks on steel surfaces by etching technique, Forensic Sci. Int. 171 (2007) 27–32]. Thus the sensitivity of the etching reagent on steel surfaces appeared to be dependent on the content of carbon in the steel.     

Restoration of engraved marks on steel surfaces by etching technique

It is known that restoration of erased engraved identification marks on the engine and the chassis of a car or on a firearm has low success rate. Unlike stamping, engraving on a metal surface leaves no pronounced, permanent subsurface deformation in the crystalline structure, also called dislocation that can be revealed by suitable methods. Hence, the current research work investigated whether metallographic reagents used in the restoration of stamp (compression) marks could be applied to recover engraved marks on steel surfaces and also to establish the sensitivity and effectiveness of some of these reagents for the restoration of the marks. Experiments were conducted by mechanically engraving alphanumeric characters on several steel plates using a computer controlled engraving machine called Gravograph. The markings were later erased from the above steel plates by removing the metal in stages of 0.01 mm through 0.04 mm below the bottom of the engraving. Several plates were thus prepared wherein each one had been abraded to a specific depth. Then eight metallographic reagents were tested on each one of the above erased plates using a swabbing technique. The results had shown that while most of the reagents were able to restore marks up to certain levels of erasure, the reagent 5 g copper sulphate, 60 ml water, 30 ml concentrated ammonium hydroxide and 60 ml concentrated hydrochloric acid restored marks erased to a depth of 0.04 mm below the engraving depth, thus presenting itself the most sensitive reagent. Quite significantly, the above reagent was also able to decipher successfully the original engraved marks that had been erased and engraved with a new number, or obliterated by centre punching. The results of this research work should benefit the forensic practitioners engaged in the serial number recovery on vehicles, firearms and other objects.     

Development of etching paste for serial number restoration on aluminum engine block

Engine numbers, which involve information regarding the engine type, production number, and year and place of manufacture, are used for identification purposes. Comprising of unique alphanumeric characters, the engine numbers are fully or partially obliterated especially in auto theft and smuggling cases to conceal the origin, identity, and owner of vehicles. The limitations of the current restoration techniques such as the difficulty of using chemical liquid etching in vertical sites, the restrictions of magnetic and optical methods, and the applicability of several techniques like electron backscatter diffraction only in the laboratory environment prompt the development of new techniques. In view of these limitations and the importance of restoring engine numbers in criminal investigations, this unique study aimed to develop an etching paste that would restore the effaced characters on a real aluminum alloy engine block. The characters which were cold-stamped on the engine block were milled at varying depths and restoration attempts were conducted using etching pastes formed with different chemicals and materials. The analyses indicate that the etching paste formed with 200 mg of perlite, 400 mg of iron powder, and 450 μL of 20 M NaOH provided restoration to a good extent. The prevention of over-etching through the controlling of the chemical reaction and the cost-effectiveness appears to be the advantages of this technique. The success of recovery on the real engine block, the facilitation of restoration on curved surfaces, and the chance of on-site usage will likely make the etching paste a widely used tool in serial number restoration.     

The recovery of finger marks from soot-covered glass fire debris.

This study aimed to expand the scope of previous research by assessing the effectiveness of soot-removal techniques on glass from petrol-bomb debris using methods of 1% and 2% sodium hydroxide (NaOH) solutions, ultrasonic bath and vacuum suction. Of particular interest were the 1% and 2% NaOH solutions applied to the soot-covered surfaces. Petrol bombs containing petrol or a 50:50 mix of petrol and motor oil were exploded and the debris was collected for analysis. Favourable results were found to varying degrees using each of the soot-removal methods with the 1% and 2% NaOH wash solutions, being the most useful. The 2% NaOH solution also proved successful as a soak to loosen and remove heavy contamination of soot and accelerants without damaging the finger mark beneath. This study also found that recovery of finger marks in blood from beneath soot using the 2% NaOH solution was possible. Finger marks were also applied to glass bottles with plastic adhesive labels, and providing the fire damage is not too great marks were also retrievable. Results from this study lead to the conclusion that the NaOH wash solution is ideally suited for soot removal to reveal latent and blood-contaminated marks both within the laboratory and at crime scenes.     

Cadmium-free quantum dots in aqueous solution: Potential for fingermark detection,synthesis and an application to the detection of fingermarks in blood on non-porous surfaces

The use of quantum dots (QDs) in the area of fingermark detection is currently receiving a lot of attention in the forensic literature. Most of the research efforts have been devoted to cadmium telluride (CdTe) quantum dots often applied as powders to the surfaces of interests.Both the use of cadmium and the nano size of these particles raise important issues in terms of health and safety. This paper proposes to replace CdTe QDs by zinc sulphide QDs doped with copper (ZnS:Cu) to address these issues. Zinc sulphide–copper doped QDs were successfully synthesized, characterized in terms of size and optical properties and optimized to be applied for the detection of impressions left in blood, where CdTe QDs proved to be efficient. Effectiveness of detection was assessed in comparison with CdTe QDs and Acid Yellow 7 (AY7, an effective blood reagent), using two series of depletive blood fingermarks from four donors prepared on four non-porous substrates, i.e. glass, transparent polypropylene, black polyethylene and aluminium foil. The marks were cut in half and processed separately with both reagents, leading to two comparison series (ZnS:Cu vs. CdTe, and ZnS:Cu vs. AY7). ZnS:Cu proved to be better than AY7 and at least as efficient as CdTe on most substrates. Consequently, copper-doped ZnS QDs constitute a valid substitute for cadmium-based QDs to detect blood marks on non-porous substrates and offer a safer alternative for routine use.     

Styryl dye coated metal oxide powders for the detection of latent fingermarks on non-porous surfaces

Conventional fingermark powders rely on contrast induced by absorption/reflection (e.g. black powder) or luminescence in the visible region (e.g. Blitz Green(?)). In most cases, these powders provide sufficient contrast; however, in some circumstances surface characteristics can interfere with the visualisation of powdered fingermarks. Visualisation in the near infra-red (NIR) region, however, has been shown to eliminate interferences commonly encountered in the visible region. In this study, a mixture of rhodamine 6G and the NIR laser dye styryl 11 (STaR 11) was coated onto an aluminium oxide nanopowder and then mixed with silver magnetic powder to develop and visualise fingermarks in the NIR. When compared to Blitz Green(?), it was determined that the STaR 11 magnetic powder was better suited for marks deposited on textured surfaces and for older marks, whereas Blitz Green(?) performed better on smooth glossy surfaces. The ability of the STaR 11 mixed dye formulation to be visualised in both the visible and NIR regions also provides a significant advantage over conventional luminescent fingermark powders.     

Visualising the past – An evaluation of processes and sequences for fingermark recovery from old documents

This study aimed to collect data on the effectiveness of most of the fingermark visualisation reagents currently used on porous surfaces on fingermarks aged for up to 90?years, significantly extending the timescales for which such information exists. A limited subset of the variables associated with processing of old fingermarks was explored, with a focus on the use of 1,8 diazafluoren-9-one (DFO), 1,2-indandione, ninhydrin, and physical developer. These techniques were used in sequence on batches of cheques between 11 and 32?years old, and on documents dating from the 1920s and 1940s. The potential for applying a physical developer enhancement process (blue toning) as the final step in the sequence was also explored. The benefits of using processing sequences on porous items were clearly demonstrated, with all processes in the sequence adding value in terms of additional marks found on the cheques up to 32?years old. In addition, physical developer was found to be capable of developing fingermarks up to 90?years old, whereas the amino acid reagents appear less effective on documents of 70?years and older. An experimental physical developer formulation with reduced environmental impact was found to be as effective as the existing process in these experiments. Blue toning was found to visualise an additional 10–25% of marks, and its wider use after silver-based deposition processes is recommended based on the evidence from this study.     

Evaluation of iodine-benzoflavone and ruthenium tetroxide spray reagents for the detection of latent fingermarks at the crime scene

The performance of two spray reagents, iodine-benzoflavone and ruthenium tetroxide (RTX), was evaluated and compared with the conventional technique currently used at the crime scene, that is, powdering. Neither the spray techniques nor powdering were shown to be suitable for all surfaces and ages of marks tested. On some surfaces such as glass and treated wood, powdering was still the superior technique, whereas the spray techniques produced better development on wallpaper, vinyl, and brick. Sequencing work showed that RTX was incompatible with powdering and cyanoacrylate (with a rhodamine 6G stain). Iodine-benzoflavone can be used successfully either before or after powdering in a sequence; however, it was incompatible with cyanoacrylate. Two non-CFC formulations of iodine-benzoflavone using HFC4310mee and HFE7100 solvents were tested and shown not to be as effective as the original Arklone (CFC-113) formulation; however, the HFC4310mee solvent is recommended as the most suitable replacement solvent. Due to the expense of the commercial RTX spray, attempts at formulating a more cost-effective version were also carried out. A formulation was developed that gave comparable development to the commercial version but at a much cheaper cost, and with a shelf life of up to two months. Recommendations are presented for which techniques are suitable for different surfaces and ages of marks. Powdering was shown to be the best technique on all ages of marks tested on treated wood, glass, and also on marks aged three days and older on paint. Iodine-benzoflavone was the best technique on wallpaper, vinyl, brick, and raw wood. RTX was the best detection technique for fresh marks and marks aged up to one day on wallpaper and paint.     

Fingerprint recovery from human skin surfaces.

A study was conducted to investigate whether certain dactyloscopic powders and reagents can recover latent fingerprints on human skin surfaces. Four fingerprint powders, Magnetic Jet Black, Magnetic Silver, Silver Special, Swedish Black, and two other methods, cyanoacrylate fuming (CA) and Ruthenium tetroxide (RTX), were used. Having examined skin surfaces with a forensic light source, we observed that the fingerprint impressions remained visible up to 15 min after intentionally placing them on the skin surface of living subjects and dead bodies. Finger marks were recovered and positive results were achieved with Magnetic Black and Swedish Black powder on living subjects. On dead bodies finger marks treated with cyanoacrylate were visible but those treated with RTX, Swedish Black and Magnetic Jet Black powder were useful for potential comparison. On dead bodies best results were obtained with RTX method.     

Influence of vertical angle of a tool on its tool mark

The paper deals with the influence of the vertical angle of a tool on the resultant tool mark. Experiments were carried out using five screwdrivers on aluminium surfaces, the vertical angle of each screwdriver being varied from 90° to 25° in steps of 5°. It was found that differences in vertical angle greater than 15° may cause non-identity between two marks from the same tool.     

Techniques for fingerprint recovery on vegetable and fruit surfaces used in Slovenia — A preliminary study

An examination was conducted to investigate whether certain dactyloscopic powders and reagents can recover latent fingerprints on vegetable and fruit surfaces (apple, banana, tomato and potato). Two fingerprint powders, Swedish Soot powder mixture (Swedish Black), Silver Special powder and cyanoacrylate fuming (CA), were investigated. The results have shown that detection with Swedish blackpowder is the most suitable procedure as the percentage finger marks which were of adequate quality for further examination, was higher than with any other technique examined.     

Luminous lip-prints as criminal evidence

Luminescence is specially a useful property for the search of invisible evidences at the scene of a crime. In the latent fingerprints particular case, there are at one's disposal fluorescent reagents for their localization. The study of latent lip prints (that is lip prints from protective lipstick, or permanent or long-lasting lipstick that do not leave any visible marks) is more recent than fingerprints study. Because of the different composition of both types of prints, different reagents have been tried out on their developing. Although, lysochromes are particularly useful reagents to obtain latent lip prints, it may occur on coloured or multicoloured surfaces, the developing is not perceived due to contrast problems between the reagent and the surface where the print is searched. Again, luminescence offers the possibility to solve this problem. Nile Red is being studied as a potential developer for latent lip prints. The results on very old prints (over 1year) indicate that this reagent is highly efficient to get latent lip prints.     

Solving underwater crimes: Development of latent prints made on submerged objects

Underwater crime scenes always present a challenge for forensic researchers, as the destructive effect of water considerably complicates the chances of recovering material of evidential value. The aim of this study is to tackle the problem of developing marks that have been left on submerged objects. Fingermark deposition was randomly made on two surfaces — glass and plastic whilst the material was submerged under tap water and then left for one to fifteen days before drying and development. For their later development, various reagents – Black Powder, Silver Metallic Powder, Fluorescent Powder, Sudan Black (powder and solution) and Small Particle Reagent – were used and the effectiveness of each of them on this particular type of evidence was then evaluated.The results show the possibility of obtaining good quality developed marks, even under such adverse circumstances. Further and wider research should, therefore, be undertaken in which other variables are introduced such as different substrates, other types of liquids, and environmental or time factors.     

Evaluation of different sampling media for their potential use as a combined swab for the collection of both organic and inorganic explosive residues

Commercially available skin cleansing alcohol wipes and conventional swabs were investigated for their use as a universal sampling medium for the simultaneous collection of both organic and inorganic explosive residues. Six compounds with the potential to be encountered in casework [pentaerythritol tetranitrate (PETN), 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), triacetone triperoxide (TATP), ammonium nitrate, and sodium chlorate] were selected as representative target compounds. Quantities of these target compounds were deposited on four different substrates (glass, plastic, aluminium foil and laminate). Two chosen alcohol wipes demonstrated better overall performance in the recovery of both the organic and inorganic representative compounds from each of the test surfaces compared to the results obtained using conventional cotton and polyester swabs, pre-moistened with various solvents, and a direct methanol wash (used as a control). Results obtained using dry cotton swabs indicated that it was not an effective swabbing system for the collection of both organic and inorganic explosive residues on common substrates.     

Molecular study of time dependent changes in DNA stability in soil buried skeletal residues

Stamp marks are used as a unique identification for a range of items, but these can be erased for criminal activities. Erased marks can sometimes be recovered by etching or magnetic means. The present study looked at the application of Fry's reagent to recover erased marks from steel. The investigation also demonstrated that Fry's reagent can deteriorate on storing and will require a longer etching time. The effect of different applied forces of stamping was investigated, and the depth of the underlying deformation was determined by etching after varying degrees of metal removal. The amount of metal needing to be removed depends on the force applied to the die. Metal removal also affects the time needed for recovery. The underlying structural change remains as a hidden identification mark, and could potentially be used by manufacturers as an unseen identifier. A model for the underlying deformation is proposed.     

The recovery of latent fingermarks and DNA using a silicone-based casting material

There are many techniques available for the recovery of fingermarks at scenes of crime including the possibility of taking casts of the marks. Casts can be advantageous in cases where other destructive recovery techniques might not be suitable, such as when recovering finger marks deposited on valued or immobile items. In this research, Isomark (a silicone-based casting material) was used to recover casts of finger marks placed on a variety of substrates. Casts were enhanced using cyanoacrylate fuming. Good quality marks were successfully recovered from a range of smooth, non-porous surfaces. Recovery from semi-porous surfaces was shown to be inefficient. DNA was subsequently extracted from the casts using QIAamp Mini extraction kits, amplified and profiled. Full DNA profiles were obtained 34% of samples extracted.     

Recovering obliterated laser engraved serial numbers in firearms

An easy procedure for recovering obliterated firearms serial numbers, which are laser engraved is presented in this case report. For these serial numbers, the traditional recovering method using acid etching generally fails, once marking the serial number does not necessarily imply a deep permanent deformation of the crystalline array. The standard required mirror-like finish of the surface commonly can destroy any evidence of the original serial number, i.e., can destroy the heat affected zone (HAZ) of only few micra, if it is still present. It is shown in this report that relief polishing and reflected light stereomicroscopy can, in certain cases, successfully reveal obliterated serial numbers, originally marked by laser. The use of this procedure for recovering this type of obliterated serial number is illustrated and discussed with an example we have dealt with.     

Chemical enhancement of soil based footwear impressions on fabric

This study investigates the enhancement of footwear impressions prepared with soils from different locations on a variety of fabric surfaces with different morphology. Preliminary experiments using seventeen techniques were carried out and the best responding reagents were evaluated further. Results indicated that the soils investigated (a cross-section of soils from Scotland) are more likely to respond to reagents that target iron ions rather than calcium, aluminium or phosphorus ions. Furthermore, the concentration of iron and soil pH did not appear to have an effect on the performance of the enhancement techniques. For the techniques tested, colour enhancement was observed on all light coloured substrates while enhancement on dark coloured fabrics, denim and leatherette was limited due to poor contrast with the background. Of the chemical enhancement reagents tested, 2,2'-dipyridil was a suitable replacement for the more common enhancement technique using potassium thiocyanate. The main advantages are the use of less toxic and flammable solvents and improved clarity and sharpness of the enhanced impression. The surface morphology of the fabrics did not have a significant effect on the enhancement ability of the reagents apart from a slight tendency for diffusion to occur on less porous fabrics such as polyester and nylon/lycra blends.