Letter to the Editor Re: XCAT (Capillary Analysis Test) Validation Study: Practical Field Use of Presumptive Gunshot Residue Test. J. For. Ident.

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1 Letter to the Editor Re: XCAT (Capillary Analysis Test) Validation Study: Practical Field Use of Presumptive Gunshot Residue Test. J. For. Ident. 2016, 66 (4), Upon review of the article, we found several technical inconsistencies as well as unfounded conclusions. Please see details outlined below: 1. The author titled the article a Validation Study. The total data set presented is 17 samples. Eleven of these 17 were included in an experiment (Experiment A) that the authors admitted may interfere with the XCAT presumptive test results. This is not a statistically significant data set to reach the conclusion that the XCAT is unreliable and should not be used in the field for presumptive GSR testing. 2. The author states that there is a possibility of crosscontamination from one GSR card to and that the XCAT cannot be properly cleaned. This statement is made with no actual evidence, and the author fails to state or recognize that the sample collection area is covered with a protective adhesive prior to insertion into the XCAT to prevent any possible cross-contamination. In fact, their own test data shows that after multiple positive samples were tested (Experiment B, 1-4), that a control was tested and a negative was achieved. The author did not indicate that the XCAT was cleaned prior to the control. This proves that there was no cross-contamination within the XCAT. The XCAT has been fielded for 4 years without any report of cross-contamination of the GSR cards. 3. The author states that the XCAT had false negatives, i.e. GSR particles are actually present. There is no way for the author to prove that the XCAT negative field test results are false without follow-up SEM analysis of the samples. No SEM analyses were conducted on any of the XCAT samples; therefore, there is no verification if GSR particles are present or not. 4. The author states, the device was inconsistent concerning the laser.. The XCAT does not have a laser. 5. The author states the XCAT was deemed to be unreliable and easily susceptible to influence by several variables, but no variables are identified (aside for their incorrect 306 / 67 (3), 2017

2 assertion of an inconsistent laser, which is untrue because the XCAT does not use a laser). It is important to note in this discussion that gunshot residue, by nature, is highly variable. 6. We absolutely concur that presumptive field test samples should be confirmed by SEM analysis prior to use in court. After all, the XCAT GSR system was designed to be a two phase process; field testing as phase 1 followed by confirmatory SEM analysis as phase 2. The author concentrated only on the phase 1 part and completely ignored the phase 2 part on all the samples. However we strongly disagree that the XCAT is not suitable for the field. The XCAT provides investigators with reliable and timely information with regard to the possible presence of GSR on hands, clothes, vehicles, etc. in the field and the ability to perform a follow-up SEM on the same sample provides a methodology for GSR detection never before available in the field. Chris Ellis, VP Sales Dr. Sarah Toal, VP Chemistry RedXDefense, LLC Rockville, MD Addendum I have personally been utilizing the XCAT in the field since March 2014 and find the XCAT to be very reliable and have used it hundreds of times in all sorts of testing conditions. I utilize the XCAT in every Shooting Reconstruction course as well as my basic and advanced crime scene investigation courses, and have had great success in over 40 courses and in actual case work. I have field tested the XCAT on not just hands of possible shooters and non-shooters but also on clothing, vehicles, towels that firearms were wrapped in, as well as very brief transient contacts of a firearm as if it were being handed to a friend to dispose of or hide. The XCAT is the only product out there that can provide reliable and real time results that can immediately aid the investigator in a shooting investigation. The field tests performed in the study that raised concerns over the fear of possible eliminating or possibly identifying a suspect with the XCAT is certainly unwarranted and not supported by their testing and is far less than the lack of data from doing a gold standard SEM adhesive stub packet and letting it sit on the shelf for a year or the state attor- 67 (3), 2017 \ 307

3 ney s office not wanting to send the packet off because the results do not tell then who the shooter is. The XCAT fills a large investigative void created by the loss of places performing SEM and the mindset that the state attorney cannot identify the shooter from a positive or negative result from the SEM. To that I respond where is the test that they normally used in the past or present, that tells them who the shooter is? I would like to personally patent that test. The XCAT gives the investigator the ability, along with their other skills and tools, the decision making power to incorporate the presence or absence of GSR by presumptive testing, available immediately in real-time, into their case strategy. The XCAT performs admirably with regards to being another essential tool in the investigator s toolbox. The XCAT is to gunshot residue as phenolphthalein is to presumptive blood testing it tells a piece of the forensic story and has the ability to be confirmed for court testimony same as a presumptive blood swab that tested positive in the field goes to DNA analysis for a profile. I too take exception to the discussion and conclusions reached and stated, by the author, within the XCAT Validation Study in Article 66 (4) 2016 of the JFI. Specifically the methods and experiments of the study employed by the author were poor in design for what was actually being tested. In Experiment A of their study of eleven participants, they purposely had each participant fire only a single shot and then waited an hour to collect a sample on a common adhesive collection stub over the entire firing hand (both back and palm area), and only then followed up with sampling with the XCAT sampling card per operating instructions. The fact that only a single discharge was fired, immediately places the testing at the lowest limit of detectability for which even the gold standard of scanning electron microscopy can also fail to detect sufficient unique particles for a positive result. The very fact that the adhesive particle collection stubbing was deployed first on the subjectʼs shooting hand, and undoubtedly sampled and collected the very GSR components that you were trying to evaluate the XCAT s ability to detect in your test, is extremely problematic to draw any conclusions from very limited test results in a poorly designed test. I do not take exception to the hour wait for sampling as that is certainly more realistic to case work but using the XCAT adhesive card over the same area that you previously sampled with your confirmatory SEM stubs is similar to showing up at the last meal of the day on Thanksgiving..the first ones eating at noon got all the good stuff.the ones showing up at 7 PM got the scraps and leftovers, or some of the best stuffing was already gone! 308 / 67 (3), 2017

4 With regards to the false negatives that were reportedly identified, additional testing needed to have been performed on a SEM to determine whether these were actual false negatives or the result of a sampling error. None of these possibilities were investigated. I agree with the other technical discrepancies listed above by RedXDefense and for the sake of space will not be repetitive of their comments. Any concerns or comments please feel free to contact me at Forensic Pieces. NOTE: Forensic Pieces does not have a financial interest in RedXDefense nor does it profit from the sale of XCATs. Janice M. Johnson President and Owner Forensic Pieces, Inc. Pensacola, FL Author s Response: Dear Editor, Thank you for the opportunity to address potential technical inconsistencies and unfounded conclusions as mentioned in the aforementioned Letter to the Editor. I would like to clarify several points brought up for discussion, as well as provide further explanation as to the development and execution of the study. Please see my below responses to the previously submitted outline, corresponding to each numbered topic: 1. The derivation of the experiment was based upon (A) a lack of data collection information available from agencies practical use in the field and (B) a requirement for a validation-type study pursuant to accreditation standards. The experiment was designed to serve as a baseline prior to deployment in the field. Purposefully chosen, the experiment reflected varied extremes, ranging from a single discharge of a firearm to approximately one hundred, for the intent of data collection. While the total number of samples was limited, the results recorded during the experiment allowed the opportunity to reevaluate the conditions under which the XCAT device may be utilized as well as the methods used for collection. Due to the narrow scope of the study, the article called for additional research to be performed, in the hopes that statistically significant data may be acquired. 67 (3), 2017 \ 309

5 2. The topic of cross-contamination was noted as a possibility due to observations made of the device and sample collection cartridge as well as based upon the author s training and personal experience of evidence collection and protection procedures. In addition, an instructional video and procedures for cleaning the XCAT (as provided by RedXDefense resources) were referenced, showing the need to properly clean the device due to possible sample residue. While the sampling cartridge for gunshot residue does contain a protective adhesive that may be folded over to protect the sampling pad, as discussed in the explanation of the recommended procedure, it does not remain secure due to a loss of adhesiveness during collection, nor is the sampling pad fully encompassing so as to completely protect the potential evidence. The XCAT was not cleaned prior to testing of the control during the experiment. In response to the suggestion that a negative control sample within this experiment, proves that there was no cross-contamination within the XCAT, due to the small sample number and lack of statistically significant data, this statement may remain undetermined. Instructional videos and procedures for cleaning the XCAT device may be viewed through the following websites: mgnjlgu2i&t=84s 3. The discussion regarding false negatives originated with Experiment B, in which an officer discharged his service weapon approximately 100 times and the XCAT red/green LED indicator identified no GSR particles present (green light). The sampling pad did indicate a color change suggesting the presence of lead; however, it was the device s inability to recognize the color change which caused concern. This suggested that the device may be unreliable. Again, SEM confirmatory analysis and additional research was suggested for further data collection. 310 / 67 (3), 2017

6 4. The laser described in the experiment referenced the process in which the unit analyzes an optical signal resulting from a chemical reaction between the sample and detection inks residing in the sampling card. At the time of publication, information provided by the manufacturer failed to specify how the internal mechanism completed the analysis. 5. Variables that were identified during the original article through discussion included: the ability to effectively clean the device, the structure and use of the sampling pad cover, and the indication from previous samples in which the XCAT s red/green LED indicator failed to identify the presumptive presence of lead. This author agrees to the highly variable nature of gunshot residue and hopes that this is kept under consideration during all presumptive and confirmatory collection and analysis procedures. 6. Due to the need to establish departmental policies regarding the XCAT device for gunshot residue presumptive testing, the scope of the study remained on the device itself and collection procedures, rather than confirmatory analysis. The study suggested the need for additional SEM confirmatory analysis to be performed, as well as additional research regarding practical collection methods in the field. Since the publication of the study, additional research has been performed, which addresses collection effectiveness. Also, the author s department has established a procedure for documenting SEM confirmatory results in which the XCAT has been used in the field. This additional information will benefit both prior and future research regarding the presumptive testing Ashleigh Newell Wojslawowicz Charleston Police Department Charleston, SC [Editor's comment: JFI Publishing Guidelines state that Letters to the Editor are brief communications that discuss a previously published paper. However, even though they are reviewed for content and significance, because of the personal or critical nature of most letters, letters and responses are not revised or subjected to the normal editing practices of the JFI.] 67 (3), 2017 \ 311