Detecting buried metallic weapons in a controlled setting using a conductivity meter

Abstract

Forensic personnel may face a daunting task when searching for buried weapons at crime scenes or potential disposal sites. In particular, it is common to search for a small firearm that was discarded or buried by a perpetrator. When performing forensic searches, it is recommended to first use non-invasive methods such as geophysical instruments to minimize damage to evidence and to the crime scene. Geophysical tools are used to pinpoint small areas of interest across a scene for invasive testing, rather than digging large areas throughout the site. Prior to this project, there was no published research that tested the utility of the conductivity meter to search for metallic weapons such as firearms and blunt and sharp edged weapons. A sample comprised of 32 metallic weapons including firearms, blunt and sharp edged weapons, and scrap metals was buried in a controlled setting to test the applicability of a conductivity meter for forensic searches. Weapons were tested at multiple depths and after data collection was performed for one depth, the weapons were reburied 5 cm deeper until they were no longer detected. Variables such as weapon size, burial depth, transect interval spacing (25 and 50 cm), and metallic composition were tested. All of the controlled variables influenced maximum depth of detection. For example, size was a factor as larger weapons were detected at deeper depths compared to smaller weapons. Metal composition affected maximum depth of detection as the conductivity meter detected items comprised of ferrous metals at deeper depths than non-ferrous metals. Searches for large buried items may incorporate a transect interval spacing of 50 cm but small weapons may be undetected between transects and therefore a transect interval spacing of 25 cm is recommended. Overall, the conductivity meter is a geophysical tool to consider when searching for larger-sized metallic weapons or to use in conjunction with an all-metal detector, particularly when searching for buried metallic evidence in obstructed areas.