Putting a Nail in the Coffin of the Hilti Defense
On December 8, 2007, Damone Jackson was shot while lying in bed at his apartment. Three bullets and three cartridge cases were found on the bed. Jackson was the landlord of his apartment complex. On December 7, 2007, Jackson evicted Rodney Evans from the house, establishing him as a prime suspect. A primer residue kit was collected off Evans and sent to the lab for analysis. The primer residue analysis indicated that the residue consisted of: antimony, barium, and lead. Primer residue is deposited onto the hands in various ways. These include but are not limited to: firing a weapon, handling a weapon, being in close proximity to a weapon being discharged, or coming into contact with an object that has primer residue on it.1 Rodney Evans was a construction worker and claimed that the primer residue came from a powder-actuated tool, also known as a Hilti gun, which was used during his construction work. Hilti is one of the main manufactures of powder-actuated tools. Hilti guns use a primer in which the propellant acts on a piston to drive a fastener into a substrate.
Evans was tried and found not guilty of 2nd degree murder. A key part of the defense was an “expert witness,” another construction worker, who said that the primer residue came from the Hilti gun. The prosecution did not present a rebuttal expert witness.
According to Wolten, et al, there are four compositions that are unique to primer residue and are therefore considered characteristic: (1) lead, antimony, and barium; (2) barium, calcium, and silicon, with a trace of sulfur; (3) barium, calcium, and silicon, with a trace of lead if copper and zinc are absent; and (4) antimony and barium.2 Some other compositions are consistent with gunshot residue but are not unique to it: (1) lead and antimony; (2) lead and barium; (3) lead; (4) barium if sulfur is absent or present only as a trace; and (5) antimony (rare).2
The researchers wanted to prove whether or not all components of primer residue were released when firing a Hilti gun. Even though Evans was found not guilty and can’t be re-tried, this study could turn out to disprove the “Hilti Defense.” The researchers’ hypothesis was that the Hilti gun would not produce all the components of primer residue given that the nail guns are low caliber. The authors’ anticipated results were that only the lead and barium components would be found in the primer residue kit analysis because test fires without the nails did not produce all three primer residue components. The fasteners used were steel, stainless steel, and galvanized steel.
Methods and Materials
An initial test firing was conducted at the Richmond Police Department. To determine the load type, .22, .25, and .27 caliber Hilti guns were fired without fasteners. The Department of Forensic Science Central Lab in Richmond, Virginia, analyzed the load samples. A light, medium, and heavy load were tested and all three resulted in having lead and barium but lacked antimony. The medium load was used for the experiment. The experimental firing took place at Hilti on Broad St. in Richmond, VA. The hands of the person firing the gun were washed prior to test firing to prevent contamination. A tyvek suit and gloves were placed on the person firing the gun to prevent any cross contamination. Ten steel fasteners were fired into a 2x4.
The hands were sampled using a sterile primer residue kit. One cartridge case was collected in a manila envelope to preserve it for primer residue analysis. Also, one steel fastener was collected in a manila envelope to preserve it for an elemental analysis exam. The hands were then washed again and a new suit and gloves were put on and the procedure was completed again using stainless steel and galvanized steel fasteners respectively. The fastener order was chosen to prevent the least amount of contamination. Hilti does not manufacture stainless steel or galvanized steel nails for the .22 or .25 caliber gun unless a custom order is placed. These samples were then sent to the Department of Forensic Science Central Lab to be analyzed on the Scanning Electron Microscope (SEM) outfitted with an energy dispersive spectroscopy (EDS). The SEM was set up to scan for any element that could be contained in each sample. An internal standard was used after each type of nail was analyzed to ensure quality assurance. A picture was captured by the SEM and the results of each spectrum were then printed out. The SEM/EDS is the ideal machine for analysis because it analyzes the particles based on their morphology and their elemental composition. In the past, testing for gunshot residue often involved chemical tests for specific elements contained in bullet or primer particles; unfortunately, these tests were prone to false positives and were hardly discriminating.3 The SEM/EDS combination allows for excellent discrimination and accurate results.
The images and EDS spectrum can be seen in the results section. The particle counts revealed that no antimony was present in any of the samples except for the .27 galvanized steel where there were two particles containing antimony, which can be expected since Wolten states that finding antimony is rare.2 The particle counts also revealed that the samples contained lead-barium, lead rich, and barium particles. According to Wolten’s classifications, then, the samples do not produce unique primer residue but are indicative of primer residue.2 The results indicate that the Hilti nail gun does not produce the same three component primer but instead produces a primer with only two components, therefore making it consistent with gunshot residue but not unique to it. In the case that brought this debate all about, Evans had tested positive for all three components of unique primer residue, thus proving the Hilti gun was not responsible for the primer residue collected after the shooting. The test may not be very discriminating between low caliber firearms, but can be discriminating between a high caliber and a low caliber firearm. Looking at this specific case from a Bayesian statistical point of view, the likelihood ratio would support the prosecution. The prosecution’s hypothesis would be that the primer residue did not come from a nail gun, while the defense maintained that the primer residue did come from the nail gun. Knowing that the three component primer residue could not have come from the Hilti gun, this study supports the hypothesis that the primer residue was from some other source.
VA Dept. of Forensic Science Central Lab for allowing the researchers to test the samples at the lab.
Scott Maye from the VA. Dept. of Forensic Science for analyzing the samples at the lab.
Detective John Graham for help with the collection of the samples.
Richmond Police Department for providing the research supplies.
Hilti Corporation and employees at the 4203 West Broad St. Richmond, VA 23230 location for allowing the researchers to test fire at the facility.
- VA Department of Forensic Science agency report form
- Wolten, G.M., Nesbitt, R.S., Calloway, A.R., Loper, G.L., & Jones , P.F. (1979). Particle Analysis for the Detection of Gunshot Residue. I: Scanning Electron Microscopy/Energy Dispersive X-Ray Characterization of Hand Deposits from Firing. Journal of Forensic Science. 24, 409-422.
- Cowan, M.E. and P.L. Purdon, A Study of the "Paraffin" Test. Journal of Forensic Sciences, 1967. 12(1): p. 18.
Blake Kinder is a graduate student at West Virginia University studying Forensic and Investigative Science. He received a B.S. in Forensic and Investigative Science with emphases in Forensic Examiner and Forensic Biology from WVU. He can be reached at Blake.Kinder@gmail.com
Eugene Provost is currently working in the Forensic Unit at the Richmond Police Department. Eugene has been with the force for 25 years, 11 of which has been served with the Forensic Unit. He can be reached at Eugene.Provost@richmondgov.com.