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Research and Technology - Forensic Science Communications - January 2008

Research and Technology - Forensic Science Communications - January 2008

January 2008 - Volume 10 - Number 1


Research and Technology

Analysis of Bank Dye Evidence and the Challenges of Daubert Hearings

Pamela C. Reynolds
Chemist/Forensic Examiner
Chemistry Unit
FBI Laboratory
Quantico, Virginia

Introduction | Background | Daubert Guidelines | Conclusion | Acknowledgments | References | Bibliography


The admissibility of scientific evidence has been affected by a Supreme Court decision made in Daubert v. Merrell Dow Pharmaceuticals (509 U.S. 579 [1993]), which led federal trial judges to become “gatekeepers” of scientific evidence. Judges are responsible for evaluating scientific testimony to determine if it is both relevant and reliable material for the case at hand. Prior to this decision, the admissibility of scientific evidence was governed predominantly by the ruling in Frye v. United States (54 App. D.C. 46, 293 F. 1013, 1014 [1923]). In Frye, the Court found that the admissibility of scientific testimony involving novel techniques must be “generally accepted within the particular field in which it belongs.” The responsibility for allowing scientific testimony relied on the opinions of scientists within the relevant field. This posed a problem for juries that did not possess the necessary knowledge for determining if the material being presented was valid or not. The Daubert decision provided the guidelines that were needed to make such an evaluation.

Subsequent to the Daubert ruling, the subject of allowing scientific testimony was readdressed and reaffirmed in two other cases, General Electric Co. v. Joiner (522 U.S. 136 [1997]) and Kumho Tire Co. v. Carmichael (526 U.S. 137 [1999]). In Joiner, the Court upheld the trial court’s gatekeeping function regarding admitting scientific evidence when an abuse of discretion is absent. In Kumho, the Court held that the gatekeeper function of the judge shall apply to all expert testimony, including that which is nonscientific.

Although the FBI Laboratory has never encountered a Daubert Daubert challenge for the analysis of bank dye-pack evidence, this article addresses how the analysis of bank dye-pack evidence can meet the challenges of a hearing.


A bank security dye pack resembles a real stack of bills that contains an electronic device disguised within a hollowed portion of the stack (Figure 1). The pack remotely activates to discharge soon after a robber exits the bank with the device. When activated, the device emits a steady aerosol stream that contains a red dye and may also emit tear gas (Figure 2). The purpose of the device is for the dye to stain the suspect, money, and other items in close proximity, and the tear gas is used to encourage abandonment of the money, thus making it easier to recover.

Figure 1 is a bank security dye pack. The stack of bills contains an electronic device disguised within a hollowed portion of the stack.

Figure 1: A bank security dye pack: a stack of bills containing an electronic device disguised within a hollowed portion of the stack

Figure 2 shows an activated dye pack. The device emits a steady aerosol stream containing a red dye meant to stain the suspect, money, and other items in close proximity.

Figure 2: An activated dye pack

Analysis of evidence related to bank robbery incidents involves the identification of chemical residues associated with a dye pack, in particular, the red dye (1-methylaminoanthraquinone [MAAQ]) and CS tear gas (orthochlorobenzalmalononitrile). The standard operating procedure performed at the FBI Laboratory involves a multistep plan that incorporates several different techniques to identify MAAQ and CS tear gas. The chemical residues first must be visualized by examining the item for red and/or pink stains or, in the case of dark items, swabbing an item with a clean swab moistened with a solvent such as methanol or acetone. Once the colored stain is isolated, it is extracted with an appropriate chemical solvent. The liquid solvent then can be analyzed by thin-layer chromatography and gas chromatography-mass spectrometry (GC-MS) in electron impact (EI) and/or chemical ionization (CI) mode.

The presence of both chemicals, MAAQ and CS tear gas, is unique to bank security devices. However, each chemical by itself can be found in other products. MAAQ previously had been used in some colored smoke grenades for the military, but those formulations have since changed. The plastics industry sometimes uses MAAQ, and it may be found in products such as automotive taillight lenses, styrene bins, and billboards. Because the dye is very stable in such matrices, it is very difficult to remove from such materials and would require a chemical extraction. MAAQ is also used as an intermediate for manufacturing solvent dyes and acid dyes. CS tear gas typically is found in law enforcement riot-control sprays. In recent years, CS has been added in very small amounts to some personal defense sprays that are available to the public.

The identification of these bank dye-pack chemicals sometimes can provide evidence linking a suspect to a bank robbery. Often during the legal proceedings, a forensic chemist is called upon to testify regarding the identification of bank dye-pack chemicals on items retrieved from the crime scene. Questions typically address how a dye pack operates, how staining occurs, and how prevalent bank dye-pack chemicals are in other products. Discussions concerning the presence of MAAQ and CS tear gas play an important role during testimony for the purpose of establishing how a red stain may come to contain one or both of those chemicals. The FBI Laboratory has been performing analysis of bank dye-pack evidence since the 1970s. In the past two years alone, FBI examiners have analyzed more than 60 bank dye cases.

Daubert Guidelines

Several factors must be evaluated to determine the reliability of the analysis of bank dye-pack evidence. The outcome of the Daubert case provided a set of guidelines that can be used to assist a judge in determining the reliability of the scientific technique being presented. Although each particular guideline does assist in determining reliability, Daubert does not require that all of these points be addressed.

Can the method be tested?

When the analysis of bank dye-pack evidence is routinely performed in a laboratory, it should be done so under the guidance of a validated standard operating procedure (SOP) that details the materials and processes that will produce a given result. When procedures are validated, they are subjected to various testing to determine if the technique is reliable and reproducible and also to determine the detection limits for a particular chemical. Positive and negative controls (known materials with an expected result) should be subjected to the same tests at the same time as the questioned specimens for comparison.

Is there a known or potential error rate?

An error rate determined by means of repetitive blind studies has not been established for this bank dye-pack evidence analysis. However, conclusions regarding the presence of bank dye-pack chemicals rely on the results of multiple tests—not just a single examination. The use of positive and negative controls ensures that reliable results are obtained. If a problem were to occur with the instrument or the method, any discrepancies should be apparent to the analyst when the results are evaluated. Controls that fail to provide the expected result indicate a problem, and the examinations should be repeated.

Are there standards controlling the technique?

The use of both positive and negative controls is necessary in any protocol involving the identification of bank dye-pack chemicals. A negative control can be a sample of the same solvent used for the questioned specimen without any other material present. If the questioned specimen has a red or pink matrix, a sample may be taken in an area away from a suspect stain, if possible. Analysis can eliminate that background as a possible source of the bank dye-pack chemicals.

Are the techniques generally accepted in the scientific community?

The primary instrumental techniques commonly involved in the analysis of bank dye-pack chemicals (i.e., thin-layer chromatography and GC-MS) are widely used not only in forensic laboratories but also in analytical laboratories from various areas of scientific industries (e.g., pharmaceutical, environmental). Hundreds of thousands of publications have presented GC-MS as a reliable identification technique. The specific techniques as they are applied to the analysis of bank dye-pack evidence have also been published in scientific journals and presented at scientific meetings.

Has it been subjected to peer review/publication?

The subject of analyzing bank dye-pack chemicals, as well as the techniques used for the analysis, has been published in a variety of literature. The Bibliography contains a representative sample of publications relating to the analysis of bank dye-pack evidence and the analytical techniques that are used in the FBI Laboratory.


The presentation of bank dye-pack evidence is an important part of the legal proceedings of a bank robbery case. The identification of bank dye-pack chemicals on evidentiary items can provide a link between the crime scene and the suspect. The FBI Laboratory, as well as state and local forensic laboratories, is routinely called upon to present its analytical findings related to bank dye-pack evidence in a court of law. This article provided a summary of pertinent information that can be used as a reference for any future Daubert hearings for bank dye-pack evidence.


This is publication number 07-02 of the Laboratory Division of the Federal Bureau of Investigation. Names of commercial manufacturers are provided for identification only, and inclusion does not imply endorsement by the FBI.


Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993).

Frye v. United States, 54 App. D.C. 46, 293 F. 1013, 1014 (1923).

General Electric Co. v. Joiner, 522 U.S. 136 (1997).

Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999).


LeBeau, M. A., Brimm, P. H., Bartholf, J., Rickenbach, M. P., Reynolds, P. C., and Mothershead, R. F. FBI Bank Security Device Workshop. Presented at the American Academy of Forensic Sciences 57th Annual Meeting, New Orleans, Louisiana, February 22, 2005.

Harrison, A. G. Chemical Ionization Mass Spectrometry. 2nd ed., CRC Press-Taylor & Francis, Boca Raton, Florida, 1992.

Hites, R. A. Gas chromatography mass spectrometry. In: Handbook of Instrumental Techniques for Analytical Chemistry. F. Settle, ed. Prentice Hall-Simon & Schuster, Upper Saddle River, New Jersey, 1997, pp. 609–626.

Jaenchen, D. E. Thin-layer (planar) chromatography. In: Handbook of Instrumental Techniques for Analytical Chemistry. F. Settle, ed. Prentice Hall-Simon & Schuster, Upper Saddle River, New Jersey, 1997, pp. 221–239.

Jagerdeo, E., Leibowitz, J. N., Schumacher, L., Henningen, D. A., and LeBeau, M. Analysis of trace amount of bank dye and lachrymators from exploding bank devices by solid-phase microextraction and gas chromatography-mass spectrometry, Journal of Chromatographic Science (2006) 44:86–90.

Kataoka, M., Seto, Y., Tsuge, K., and Noami, M. Stability and detectibility of lachrymators and their degradation products in evidence samples, Journal of Forensic Sciences (2002) 47:44–51.

Martz, R. M., Reutter, D. J., and Lasswell, L. D. III. A comparison of ionization techniques for gas chromatography/mass spectroscopy analysis of dye and lachrymator residues from exploding bank security devices, Journal of Forensic Sciences (1983) 28:200–207.

Saferstein, R. Criminalistics: An Introduction to Forensic Science. 5th ed., Prentice Hall-Simon & Schuster, Englewood Cliffs, New Jersey, 1995, pp. 133–137, 145–150.

Seiden, H. Removal of dye-pack stains on U.S. currency: A reconstruction, International Journal of Forensic Document Examiners (1996) 2:220–225.

Verweij, A. M. A. and Lipman, P. J. L. Comparison of mass spectrometric techniques for the analysis of trace amounts of 1-methylaminoanthraquinone, used as smoke dye in exploding money suitcases, Journal of Chromatography A (1993) 653:359–362.

Watson, J. Mass spectrometry of volatile analytes. In: Handbook of Instrumental Techniques for Analytical Chemistry. F. Settle, ed. Prentice Hall-Simon & Schuster, Upper Saddle River, New Jersey, 1997, pp. 567–587.

Yinon, J. Miscellaneous forensic applications of mass spectrometry. In: Forensic Mass Spectrometry. J. Yinon, ed. CRC Press, Boca Raton, Florida, 1987, pp. 206–209.