Examination of writings concealed by black pressure sensitive adhesive tape

Examination of concealed writing is often a challenge for forensic document examiners. Although the published literature describes many techniques, these are often only successful when the writing has been concealed by pencil, pen, or by spreading inks of different tint or by smearing of the writing with colored fluids. When black pressure sensitive adhesive (PSA) tape is used, these procedures are ineffective. The present report describes the use of a straight chain hydrocarbon to remove the PSA tape and allow a comparison of the concealed writing with that of a suspect. The use of the solvent had no observable effect on either the writing or the substrate. The procedure is rapid and easy to use and is also effective with other colored PSA tapes.     

Analysis of pressure sensitive adhesive tape: I. Evaluation of infrared ATR accessory advances

Attenuated total reflection (ATR), also known as internal reflection spectroscopy (IRS), is a forensically accepted method for infrared (IR) analysis of pressure sensitive adhesive tapes. Advancements of ATR accessories in the last decade have provided the forensic examiner several ATR methods to choose from. These accessories offer a variety of ATR crystal choices with a variety of prices and capabilities. Four different types of pressure sensitive adhesive tapes including duct tape, electrical tape, packaging tape and office tape have been used to compare six different ATR methods. Each of the methods tested offers both benefits and limitaltions which must be considered for the type of sample to be analyze. The intent of this paper is to assist the reader in better understanding ATR techniques, the many differences among currently available ATR accessories and how the method is applied to the analysis of pressure sensitive adhesive tape.     

Applicability of DNA analysis on adhesive tape in forensic casework

Adhesive tape is commonly used in crimes and is often the subject of forensic evaluation. DNA analysis of adhesive tape can provide DNA profiles of suspects. The object of this study was to evaluate the applicability of DNA analysis on adhesive tape samples in forensic casework. We retrospectively reviewed all cases involving adhesive tape or similar items received by our institute for DNA analysis during the past 11 years. From 100 forensic cases reviewed, 150 adhesive tape samples were examined. A total of 98 DNA profiles were obtained from these samples. Sixty-two of the profiles provided feasible case-relevant information. In conclusion, DNA profiling of adhesive tape samples can be useful in a variety of forensic cases.     

Selection of an adhesive tape suitable for forensic fiber sampling

Five commercial adhesive tapes were tested for fiber uptake and saturation, for recovery and for ease of analysis. On the basis of the results, a high tack adhesive tape has been selected to be used for forensic fiber sampling. This adhesive tape is used as sampling material in two different micro trace kits. The first tape lifting kit is used mainly for the sampling of cars and the second is a 1:1 tape lifting kit for the collection of fibers on a corpse.     

Forensic utility of carbon isotope ratio variations in PVC tape backings

Forensic interest in adhesive tapes with polyvinyl chloride (PVC) backings (electrical tape) derives from their use in a variety of illicit activities. Due to the range of physical characteristics, chemical compositions, and homogeneity within a single roll of tape, traditional microscopic and chemical analyses can offer a high degree of discrimination between tapes, permitting the assessment of potential associations between evidentiary tape samples. The carbon isotope ratios of tapes could provide additional discrimination among tape samples. To evaluate whether carbon isotope ratios may be able to increase discrimination of electrical tapes, particularly with regards to different rolls of tape of the same product, we assessed the δ(13)C values of backings from 87 rolls of PVC-based black electrical tape (~20 brands, >60 products) Prior to analysis, adhesives were removed to prevent contamination by adhering debris, and plasticizers were extracted because of concern over their potential mobility. This result is consistent with each of these tapes having approximately the same plasticizer δ(13)C value and proportion of carbon in these plasticizers. The δ(13)C values of the 87 PVC tape backings ranged between -23.5 and -41.3 (‰, V-PDB), with negligible carbon isotopic variation within single rolls of tape, yet large variations among tape brands and tape products. Within this tape population, carbon isotope ratios permitted an average exclusion power of 93.7%, using a window of +/-0.3‰; the combination of carbon isotope ratio measurement with additional chemical and physical analyses raises the discrimination power to over 98.9%, with only 41 out of a possible 3741 pairs of tape samples being indistinguishable. There was a linear relationship between the δ(13)C value of tape backings and the change in δ(13)C value with the extraction of plasticizers. Analyses of pre- and post-blast tape sample pairs show that carbon isotope signatures are within 0.3‰ of pre-blast values, indicating that carbon isotope values are largely preserved during an explosion.     

Paint and tape: collection and storage of microtraces of paint in adhesive tape

The collection and preservation of microtrace evidence with the aid of an adhesive tape is a method of choice in forensic science. This technique is rapid and easy and allows the concentration of microtraces on a carrier, which facilitates further investigations in the laboratory. Adhesive tapes are currently used to secure microtraces of fibers and glass, but hardly for traces of automotive paint and other lacquers for fear of interference with the analysis of binders. A collection of automotive paint consisting of original and repair lacquers collected by tape has been evaluated. After various times of storage within the tape, these samples were compared with untreated references by microscope FT-IR and microspectrophotometry (MSP). Another set of paints was collected in 1984, stored within the tape until 1995, and examined the same way. About 170 layers of lacquer with various types of binder were examined. With the exception of one clear lacquer no difference between treated samples and references was detected. This small difference observed could be correlated to the exposure to xylene (extractant) and was not caused by the storage within the adhesive tape.     

Identification of pressure-sensitive adhesive polypropylene tape

Identification of colorless, transparent, pressure-sensitive adhesive polypropylene tape (PP tape) was performed using infrared absorption spectrometry (IR) and pyrolysis gas chromatography mass spectrometry (Py-GC/MS) to determine the pressure-sensitive adhesive. Twenty different products of colorless, transparent PP tapes were examined in this study, and the results of analysis of IR spectra and Py-GC/MS were classified into twelve groups. In addition, the tapes were classified into 14 groups on the basis of IR measurement of release agent present in the backside. The results indicate that colorless, transparent PP tapes can be distinguished in terms of manufacturer, thereby demonstrating that this method of identifying colorless, transparent PP tape is effective. Moreover, the method was applied to the analysis of an actual forensic sample.     

Adhesive tape analysis: establishing the evidential value of specific techniques

This study investigated the evidential value of specific methods of analysis for packaging tapes and clear adhesive tapes available in Australia. Fifty-eight adhesive tapes were analyzed using a wide range of optical, physical, and chemical techniques. The results were collated for the purpose of creating an Australian database of adhesive tapes, which would be of assistance in criminal investigation. Each technique was evaluated for its discriminating power, both for comparative purposes and for the identification of adhesive tapes by comparing unknown samples with the database. The combined discriminating power of the techniques applied is very high. It is possible to individually identify the source of an unknown adhesive tape sample in many instances by searching the database. It is also possible to form an opinion on the significance of a failure-to-discriminate result in comparative casework. Further work is still needed to expand and update the database, as well as compiling data on the relative market share of various products.     

Raman identification of drug of abuse particles collected with colored and transparent tapes

Raman microscopy is a useful tool for the analysis of drug particles collected with adhesive tapes. In this work, first, the spectra of thirty drugs of abuse, degradation products, metabolites, and common cutting agent standards were recorded and the Raman bands observed were summarized providing the forensic analyst useful information for the identification of drug evidence. Then, the collection of different drug particles by a fingerprint lifting tape commonly used to remove and store fingerprints and fibers, and a white and green packaging tape, followed by the subsequent identification of the drugs by confocal Raman spectroscopy was performed. The particles were analyzed on top of the tapes, trapped between glass slides and the tapes, trapped in the tape folded over itself in the case of the transparent tape, and after folding and unfolding the tape in the case of the colored tape. The results obtained by the different approaches show that both tapes did not compromise the drugs spectra. However, the use of transparent tape is preferred because this tape allows the previous visual detection of the particles. Finally, several drug and sugar particles were spread over a clean table and inside a pocket, and the particles were collected with transparent tape and then properly identified. Although good results were obtained in both cases, the amount of fibers and other substances present in the collection area made the previous detection of the particles difficult and increases the analysis time.     

透明胶带的厚度检验

目的研究不同品牌透明胶带的区分方法。方法利用测厚仪对35种不同品牌透明胶带的厚度进行检验,并对所得数据进行统计分析。结果 35种品牌透明胶带组成的595组样品对中有458组可以区分,区分率为77.0%。结论厚度检验法能够在一定程度上区分不同品牌的透明胶带,厚度检验结果可与化学成分检验相互佐证,使得鉴定结论更加准确可靠,为法庭科学领域透明胶带物证的区分提供了一种预检验方法。     

掺杂Cd的水溶性荧光ZnSe/MPA量子点显现胶带手印方法

目的探索水溶性荧光量子点溶液——掺杂镉的硒化锌（ZnxCd（1-x）Se）对胶带手印的显现方法。方法以巯基丙酸（MPA）为修饰剂合成了掺杂Cd的水溶性荧光ZnSe/MPA量子点,利用它显现水浸胶带及粘连胶带上的油汗指印,并在365nm下拍照成像。结果良好的显现出水浸胶带上的指印以及粘连胶带上的指印。与常规方法相比,优势更为明显。结论水溶性荧光量子点ZnxCd（1-x）Se溶液显出的指印纹线细腻流畅,在法庭科学领域具有很好的应用前景。     

Optimisation of cellular DNA recovery from tape-lifts

Adhesive tape-lifts are a commonly used technique for the recovery of DNA from forensic exhibits. Examination of large forensic exhibits or tape-lifts from old “cold” cases can make the direct submission of the tapes for extraction difficult. By applying a swab loaded with an organic solvent to the tape-lift, any DNA bound to the tape can be transferred and concentrated on to the swab head. Whilst removing any DNA, the tape's glue adhesive is also transferred. This requires a modified extraction technique that can dissolve the adhesive whilst maintaining the integrity of any DNA. Of several solvents tested, xylene was shown to be the solvent of choice, efficiently removing the adhesive and any bound DNA. A modified chelex extraction method, again incorporating xylene, provided optimal conditions for dissolving the adhesive and releasing the DNA for lysis.     

Atomic force microscopic investigation of commercial pressure sensitive adhesives for forensic analysis

Pressure sensitive adhesive (PSA), such as those used in packaging and adhesive tapes, are very often encountered in forensic investigations. In criminal activities, packaging tapes may be used for sealing packets containing drugs, explosive devices, or questioned documents, while adhesive and electrical tapes are used occasionally in kidnapping cases. In this work, the potential of using atomic force microscopy (AFM) in both imaging and force mapping (FM) modes to derive additional analytical information from PSAs is demonstrated. AFM has been used to illustrate differences in the ultrastructural and nanomechanical properties of three visually distinguishable commercial PSAs to first test the feasibility of using this technique. Subsequently, AFM was used to detect nanoscopic differences between three visually indistinguishable PSAs.     

Identification and Comparison of Electrical Tapes Using Instrumental and Statistical Techniques: II. Organic Composition of the Tape Backing and Adhesive*

Abstract: The microtexture and elemental composition of the backing of electrical tapes have been shown to be highly discriminating. In this study, the organic composition of electrical tape was evaluated as a complementary means of distinguishing tape brands. The backing and adhesive of 72 rolls of electrical tape were analyzed via Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR FTIR) and discriminant analysis was used to classify all samples by brand. Generally, the accuracy for FTIR data (88–99%) was higher than that for elemental data (86–94%). FTIR spectra from the adhesive layer were the most discriminating. In separate studies, two fragments of blast-damaged tape were correctly assigned to their brand of origin and discriminant analysis was used to quantitatively associate or exclude tape samples from two bombing cases.     

Visualising latent DNA on tapes

This study reports a simple method for visualising and screening latent DNA on tapes using a Diamond™ dye (DD) staining process followed by visualisation using a portable fluorescence microscope. Ten types of tapes were tested, which include those used currently by forensic laboratories for tape-lifting. All ten types were tested for: 1) their auto-fluorescence, 2) properties when stained with DD using three different DD solutions, and 3) PCR inhibition through a direct STR amplification technique. No background fluorescence was noted viewing four types stained with 20 x DD diluted with 0.01% Triton-X. Clear tape (Sellotape®), DNA-free tape (Lovell Surgical Solutions) and brown packing tape (Packmate™) did not inhibit direct STR amplification, while the other six types showed the inhibition of the PCR. The three tapes were selected to assess their cellular material recovery efficiency by comparing the number of stained cells within an entire fingermark before and after tape-lifting. Tape-lifting was performed either once, twice or ten times. The DNA-free tape (Lovell) used in many forensic laboratories gave poor recovery compared to the clear tape (Sellotape®) and brown packing tape (Packmate™). This simple visualising technique allows the cell location to be recorded, and only the area of tape where cells are present to be removed for DNA typing. The process is a simple and effective triage procedure that reduces the processing of tape-lift samples where there are no cells present.     

Isotope ratio mass spectrometry as a tool for forensic investigation (examples from recent studies).

The versatility of isotope ratio mass spectrometry is demonstrated by reference to diverse case studies. Variations in the natural isotopic composition of non-biological, organic materials are compared as a means by which samples may be associated or discriminated. These techniques may be used to augment or compliment conventional forensic methodologies. delta13C analysis was used to demonstrate that different masking tape had been recovered in two, apparently similar cases, involving the smuggling of money. Visually similar ecstasy tablets were compared by consideration of the delta13C and delta15N composition of MDMA extracted from the tablets. Although only a limited number of tablets were analysed, the isotopic similarity between two different seizures was sufficient to induce a guilty plea from a person suspected of possessing both. A combination of delta2H, delta13C, delta15N and delta18O together with GC-MS analyses were applied to small samples of seized heroin. Although GC-MS analysis indicated differences between the chemical composition of two of the heroin samples, isotopic analysis suggested similarities, which were confirmed by further delta2H, delta13C and delta18O isotopic analysis of the clingfilm in which the samples were wrapped.     

The role of isotope ratio mass spectrometry as a tool for the comparison of physical evidence

This paper considers how likelihood ratios can be derived for a combination of physical, chemical and isotopic measurements. Likelihood ratios were formulated based on the characteristics of a small convenience sample of 20 duct tapes. The propositions considered were:

• H_ptwo samples are from the same batch
• H_dtwo samples are from different batches.

The physical and isotopic characteristics of ten rolls of duct tape were shown to be consistent throughout each roll.The width and thickness of the tapes and the density of the scrim fibres provided equivalent information and the combined physical characteristics provided a basis upon which to discriminate between many of the samples.Scatter-plots and confidence ellipses provided a convenient method to group the isotopic composition of the tape backing material and provided a basis to discriminate between samples which were physically indistinguishable. Considering both the physical and isotopic characteristics it was possible, at best, to ascertain that the evidence provided moderately strong support for the proposition that two samples of tape were derived from the same batch (LR = 400).Kernel density estimates were used to model the distribution of isotopic compositions of the backing material. Using this technique it was possible to estimate objectively the probability that a sample with given characteristics could be drawn, at random, from the background population and to calculate a likelihood ratio based on the propositions above.The strength of evidence which could be presented by either model was ultimately limited by the size of the background sample.     

The Use of Adhesive Tape for Recovery of DNA from Crime Scene Items

Abstract: The selection of the appropriate method of collection of biological material from crime scene items can be crucial to obtaining a DNA profile. The three techniques commonly used for sampling items are: cutting, swabbing, and taping. The tape sampling technique offers an advantage, in that it enables the collection of a potentially highly informative source of DNA, shed epithelial cells, from selected areas on crime scene items (the inside fingers of a glove, for instance). Furthermore, surface collection of biological material by taping reduces co‐sampling of known PCR inhibitors such as clothing dyes. The correct choice of tape for crime scene item sampling is important. Not all tapes are suitable for biological trace evidence collection as well as DNA extraction. We report on one tape that met both these criteria. Three different cases are presented which demonstrate the usefulness of adhesive tape sampling of crime items. Finally, the advantages of the tape collection technique are discussed and guidelines for preferred areas of tape sampling on various casework items are presented.     

SEM-EDS analysis and discrimination of forensic soil

Soils vary among different areas, and have some characteristics because of the natural effects and transfers made by human and other living beings in time. So that forensic examination of soil is not only concerned with the analysis of naturally occurring rocks, minerals, vegetation, and animal matter. It also includes the detection of such manufactured materials such as ions from synthetic fertilizers and from different environments (e.g., nitrate, phosphate, and sulfate) as environmental artifacts (e.g., lead or objects as glass, paint chips, asphalt, brick fragments, and cinders) whose presence may impart soil with characteristics that will make it unique to a particular location. Many screening and analytical methods have been applied for determining the characteristics which differentiate and discriminate the forensic soil samples but none of them easily standardized. Some of the methods that applied in forensic laboratories in forensic soil discrimination are the color comparison of the normal air-dried (dehumidified) and overheated soil samples, macroscopic observation, and low-power stereo-microscopic observation, determination of anionic composition by capillary electrophoresis (CE), and the elemental composition by scanning electron microscope (SEM)-energy dispersive X-ray spectrometer (EDS) and other high sensitivity techniques. The objective of this study was to show the effect of the application of 9 tonnes/cm2 pressure on the elemental compositions obtained by SEM-EDS technique and comparing the discrimination power of the pressed-homogenized and not homogenized forensic soil samples. For this purpose soil samples from 17 different locations of Istanbul were collected. Aliquots of the well mixed samples were dried in an oven at 110-120 degrees C and sieved by using 0.5 mm sieve and then the undersieve fraction(<0.5 mm) of these samples put on an adhesive tape placed on a stub. About 100-150 mg aliquots of dried, sieved samples were pressed under 9 tonnes/cm2 pressure by KBr disk preparation apparatus of an infrared spectrophotometer. Surfaces of the randomized particles and the pressed disks of the soil samples were scanned and the elemental compositions were determined with scanning electron microscope JEO-JSM-5600 equipped with an energy dispersive X-ray spectrometer OXFORD Link-ISIS-300. The samples from top of the sieves were examined with stereo-microscope equipped with JVC-TK-128DE color video camera and JVC-GV-PT2, digital video printer. Natural and artificial materials that have characteristic features were identified. Then for additional confirmation all soil samples were dried at 120 degrees C and over 780 degrees C and their colors compared. We concluded that pressing the whole sieved soil samples under 9 tonnes/cm2 pressure results in smashing over the harder particles into the softer matrix and results in homogenization of the soil sample. The elemental compositions of these samples obtained by SEM-EDS with 10-fold less standard deviation (S.D.) values and so that with more reproducibility and discrimination power.     

Fingerprints and DNA: STR typing of DNA extracted from adhesive tape after processing for fingerprints

An exhibit that is often received for examination in cases of robbery or terrorist activity is adhesive tape. This type of exhibit can often, but not always, be successfully processed for fingerprints. The question arises whether or not it is possible to extract and type DNA after the tape has been sequentially processed for fingerprints. In this work, various donors left fingerprints on the adhesive side of tapes. The tapes were then sequentially processed for fingerprints using an alternate light source, cyanoacrylate fuming, and staining with BY-40 and then crystal violet. DNA was subsequently successfully extracted, amplified and typed for six STR loci.