Forensic Spotlight
Paint and Plastic Evidence Analysis in a Drug Possession Case
By Diana Wright, Ph.D.
The Forensic Spotlight is a new department in the FBI Law Enforcement Bulletin (LEB) that highlights current and noteworthy developments in the forensic sciences. Articles in the Forensic Spotlight focus on topics such as fingerprinting, ballistics, toxicology, paint analysis, document validity, and other laboratory-based technology used in crime solving. Laboratories willing to share new and interesting information in the various fields of forensic science can submit their articles to the LEB at leb@ic.fbi.gov for review and possible publication in the Forensic Spotlight.
In a case involving charges of cocaine possession with intent to supply and conspiracy to export a controlled substance, officers observed an individual who was under investigation receiving a bag from another person and wheeling it into an airport restroom. When the officers detained and searched the suspect, they found small, heat-sealed plastic bags camouflaged with black spray paint tucked inside the individual’s clothing.
The suitcase the individual took into the restroom contained a backpack filled with various items, including a tote bag. In contrast to the backpack, the tote was empty except for flakes of black paint and clumps of white powder. Based on these findings, the arresting officers concluded that the handmade, plastic drug packages were removed from the bag and placed inside the individual’s clothing, which would enable the suspect to walk the drugs through customs. They determined that once the individual cleared customs the packages would have been placed back in the tote bag within the suitcase and passed on for transport.
The next day officers searched the home of a known drug trafficker. Police seized five cans of black spray paint and rolls of heat-sealing, plastic food-storage packaging from the residence, along with a cardboard box lid containing overspray of black paint. The officers believed this was where the drugs were packaged and camouflaged for transport and eventual distribution.
Analysis Request
The police requested the assistance of the FBI’s Laboratory Division to compare the contents of the black spray-paint cans with the paint on the recovered drug packaging and the roll of plastic material. The division’s Chemistry Unit accepted the request for analysis with the caveat that black spray paint generally contains a limited number of features for comparison and that plastic-roll bags contain even fewer characteristics to provide meaningful results. However, two independent parameters could be compared, and discrimination would be a straightforward process if the items had different physical or chemical properties.
Spray Paint
In common use, whether for a household project or criminal purposes, black spray paint is relatively unremarkable. It usually is applied as a single layer, based on one of several common chemical formulations, comprised of carbon black as the primary pigment, and mass-produced for retail sale. Based on the limited number of features available for comparison, black spray paint cannot be sourced exclusively to a particular can, brand, or manufacturer. However, it can be discriminated if the spray paints contain different physical (e.g., sheen or gloss) or chemical (e.g., binder or pigment) characteristics.
The seized bags were sprayed with two distinct layers of black paint, which contained some metallic flakes to enhance the visual appeal of the coating (figure 1). One of the layers contained a metallic flake distribution that resembled automotive refinish paint. The chemical analysis of both layers was straightforward but did not indicate a manufacturer or use for the spray paint. The paint in the cans contained different chemical formulations than either of the paint layers on the bags; however, the paint flakes from the suspect’s clothing were indistinguishable from the paint on the plastic bags.
Figure 1
There are several important factors when assessing the significance of this conclusion. First, not all black spray paints are metallic, nor do all black, metallic spray paints contain the same relative distribution of metal flakes. Second, there were two distinct and independent layers of black, metallic spray paint present in this evidence. Third, two layers of black, metallic spray paint were recovered from the bags that were made of a nonconventional surface not amenable to coatings. From a drug chemist’s identification of cocaine as the white powder in the tote bag and clothing, it is logical to infer that the plastic bags were camouflaged drug packaging coated with paint to hide the contents.
Plastic Packaging
The plastic packaging used to store the drugs differed in physical appearance from most plastic films submitted for analysis. Both rolls of plastic were multilayered with a patterned side and a smooth side. The rolls differed from one another in the patterns used—a crosshatch pattern on one and a scalloped pattern on the other.
It would be common to find single-layer plastic trash bags in any residence; however, the type of plastic packaging recovered in this case was intended for long-term food storage, which is common in regions with short growing seasons. It is unknown how common long-term food storage is in the area where the crime originated.
From the residence officers obtained two rolls of plastic bagging material and two strips of this plastic cut into sheets. The sheets corresponded to one of the rolls of plastic—each had a smooth side and a patterned side, one scalloped and the other a crosshatch pattern. The rolls were on cardboard inserts, one white and the other brown, with no name brand, distributor, or manufacturer information on the core.
Because the crosshatch-patterned packaging was not among the recovered bags from the arrest, only the scalloped packaging was analyzed and compared. Chemical analysis of both sides indicated that it consisted of two different polymers—the smooth side was nylon, and the scalloped side was polyethylene. There is nothing remarkable about either polymer, and both are used in a variety of mass-produced materials. However, it is not common to find them used together in plastic packaging where the polyethylene is molded with a scalloped pattern.
Examination Results
Two different items were submitted for analysis—black spray paint and plastic packaging. It first seemed that neither of these materials had probative value because they are prevalent in the marketplace, accessible to anyone, and legal to own. Classes of materials, such as these, are common and often produced in a variety of forms to gain market share or meet consumer needs.
Forensic examinations can capitalize on the subtle differences in these materials to distinguish them. However, in the absence of any detectable physical or chemical differences, a conclusion of consistency could be reported. The challenge is to ensure that the forensic report provides context to those conclusions as a preventive measure against erroneous assumptions. For example, it would be incorrect to infer that the results are meaningless because the materials are so readily available. It also is inappropriate to conclude that no observed differences imply exclusivity or uniqueness.
For this case the report kept the materials separate and provided individual associations so that each could be assessed independently. Because some of the analyzed paint was located on the packaging, it was not as critical to report each examination separately. The materials required different analytical techniques for comparison. The results were interpreted and reported separately. From an investigative or legal standpoint, this approach could prevent loss of the entire forensic examination if some portion of the evidence was ruled inadmissible by the court.
An interpretation scale is included with every report to provide context to the stated conclusions. It was noted in the original report that the presence of two separate materials in common between the questioned items and the known materials increased the overall significance of the stated findings. The existence of an association between the paint chips recovered from the various locations and the polymeric films used as plastic bags could increase the significance of the reported associations.
The Case
At the trial, the defense attorney never mentioned the scale (despite being exposed to it during a previous case), the report findings, the limitations inherent in class evidence associations, or the known paints that were discriminated. The attorney’s focus was on the chain of custody between police and FBI laboratories. There was no jury, and testimony was provided for the benefit of a magistrate who would render the verdict.
There are several important factors when assessing the significance of this conclusion. First, not all black spray paints are metallic, nor do all black, metallic spray paints contain the same relative distribution of metal flakes. Second, there were two distinct and independent layers of black, metallic spray paint present in this evidence. Third, two layers of black, metallic spray paint were recovered from the bags that were made of a nonconventional surface not amenable to coatings. From a drug chemist’s identification of cocaine as the white powder in the tote bag and clothing, it is logical to infer that the plastic bags were camouflaged drug packaging coated with paint to hide the contents.
Plastic Packaging
The plastic packaging used to store the drugs differed in physical appearance from most plastic films submitted for analysis. Both rolls of plastic were multilayered with a patterned side and a smooth side. The rolls differed from one another in the patterns used—a crosshatch pattern on one and a scalloped pattern on the other.
It would be common to find single-layer plastic trash bags in any residence; however, the type of plastic packaging recovered in this case was intended for long-term food storage, which is common in regions with short growing seasons. It is unknown how common long-term food storage is in the area where the crime originated.
From the residence officers obtained two rolls of plastic bagging material and two strips of this plastic cut into sheets. The sheets corresponded to one of the rolls of plastic—each had a smooth side and a patterned side, one scalloped and the other a crosshatch pattern. The rolls were on cardboard inserts, one white and the other brown, with no name brand, distributor, or manufacturer information on the core.
Because the crosshatch-patterned packaging was not among the recovered bags from the arrest, only the scalloped packaging was analyzed and compared. Chemical analysis of both sides indicated that it consisted of two different polymers—the smooth side was nylon, and the scalloped side was polyethylene. There is nothing remarkable about either polymer, and both are used in a variety of mass-produced materials. However, it is not common to find them used together in plastic packaging where the polyethylene is molded with a scalloped pattern.
Examination Results
Two different items were submitted for analysis—black spray paint and plastic packaging. It first seemed that neither of these materials had probative value because they are prevalent in the marketplace, accessible to anyone, and legal to own. Classes of materials, such as these, are common and often produced in a variety of forms to gain market share or meet consumer needs.
Forensic examinations can capitalize on the subtle differences in these materials to distinguish them. However, in the absence of any detectable physical or chemical differences, a conclusion of consistency could be reported. The challenge is to ensure that the forensic report provides context to those conclusions as a preventive measure against erroneous assumptions. For example, it would be incorrect to infer that the results are meaningless because the materials are so readily available. It also is inappropriate to conclude that no observed differences imply exclusivity or uniqueness.
For this case the report kept the materials separate and provided individual associations so that each could be assessed independently. Because some of the analyzed paint was located on the packaging, it was not as critical to report each examination separately. The materials required different analytical techniques for comparison. The results were interpreted and reported separately. From an investigative or legal standpoint, this approach could prevent loss of the entire forensic examination if some portion of the evidence was ruled inadmissible by the court.
An interpretation scale is included with every report to provide context to the stated conclusions. It was noted in the original report that the presence of two separate materials in common between the questioned items and the known materials increased the overall significance of the stated findings. The existence of an association between the paint chips recovered from the various locations and the polymeric films used as plastic bags could increase the significance of the reported associations.
The Case
At the trial, the defense attorney never mentioned the scale (despite being exposed to it during a previous case), the report findings, the limitations inherent in class evidence associations, or the known paints that were discriminated. The attorney’s focus was on the chain of custody between police and FBI laboratories. There was no jury, and testimony was provided for the benefit of a magistrate who would render the verdict.
Conclusion
This case provides an example of paint and plastic evidence that previously could have been thought to be nonprobative, but was found to contain sufficient comparative characteristics and unusual features to aid in providing context to the reported results. This example serves as a means to convey how such evidence would be reported and interpreted for the court.
This case provides an example of paint and plastic evidence that previously could have been thought to be nonprobative, but was found to contain sufficient comparative characteristics and unusual features to aid in providing context to the reported results. This example serves as a means to convey how such evidence would be reported and interpreted for the court.
Dr. Wright serves in the Chemistry Unit of the FBI’s Laboratory Division in Quantico, Virginia.
The FBI Laboratory Division’s Chemistry Unit is available for any sworn law enforcement agency or court officer to discuss examination requests or capabilities and may be contacted at 703-632-8441. Agencies and individuals should refer to the Handbook of Forensic Services at www.fbi.gov for a complete listing of the examination services provided by the division’s respective laboratory units.
“Forensic examinations can capitalize on the subtle differences in these materials in order to distinguish them.”