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Module 7: Equipment & Instrumentation - Coggle Diagram
Module 7: Equipment & Instrumentation
Standards & Measurements & Accuracy
examining physical evidence requires observation, measurement, various testing methods if needed, and documentation to help determine if the piece of evidence has or could come from a common source
weight
dimensions
velocity
lab protocols are used to determine which measurements and testing are required/appropriate, but there are many reliable and correct ways to go about that
accurate results, lab accreditation, as well as certification of the firearm examiner all have effects on the ability of the examiner to take accurate measurements
when measuring weights and dimensions in a forensic case, it's important that they should be standardized and fall within guidelines maintained by the National Institute of Standards and Technology (NIST)
Reference Resources
Association of Firearm and Toolmark Examiners
Scientific Working Group for Firearms and Toolmarks
Integrated Ballistics Identification System (IBIS)
used for computer-based comparisons or correlations
MatchPoint Plus
used for on-screen side-by-side comparison
BulletTRAX-3D System
allows for preliminary correlations prior to microscopic comparisons
Measurement Equipment for Weight and Force
digital scales are commonly used to weight small objects, and are generally considered accurate, more convenient, and less costly than other options
composed of strain gauges, a load cell, a signal amplifier, and a specialized microprocessor
trigger pull weights can be used to determine the amount of force that must be applied to a trigger of a firearm to cause sear release
trigger pull generally ranges anywhere from 3 to 15 pounds depending on the type of firearm, but there may be exceptions to those ranges
trigger pull can be measured with standard trigger weights (often used by gunsmiths), spring gauges, and mechanical testers
weight is used to express the force of gravity on an object and is a convenient, standardized reference for forensic scientists
Firearm & Toolmark Examination Equipment
microscopes
comparison microscopes
stereomicroscopes
compound microscopes
digital measurement equipment
electronic reticules
mouse-driven point-to-point techniques
digital micrometers
steel machinists scale
reticules - a grid or pattern lines placed in the focus of a lens to establish a frame of reference for measurement
glass measuring reticules compatible with microscope eyepieces
filar micrometer eyepieces used for taking linear measurements on stereo and comparison microscopes; often used for land and groove impressions measurements in fired bullets
electronic reticules combine a stereomicroscope, a digital camera, and a computer for a digital overlay
calipers
personal protective equipment
small tools for general use
small file set
hammers
bench block
borescope
gunsmith screwdriver set
pliers
Firing Facilities
indoor range
used for firearms functioning testing
bullet recovery system
used for obtaining known standards for comparisons with evidence bullets
cotton boxes
water recovery tanks
outdoor range
used for testing longer distance shot patterns
Imaging Systems
film imaging
early comparison microscopes often had large cameras mounted that used fine grained black and white cut films as well as photographic plates to create photomicrographs; film needed to be developed to get an image
Polaroid cameras developed in the 1950s allowed for immediate imaging, although film was expensive
digital imaging
higher quality images became more available as digital cameras became more affordable and versatile in the 1990s, and allowed images to be converted to files for insertion in a document
image storage, image enhancement, image overlay, side-by-side comparisons, and image file export are often seen on current comparison microscopes
imaging is often a useful and convenient way of documenting identifications, but sketches and narrative documentation are also used when needed
Equipment for Field Support
it is sometimes required for firearms/toolmarks examiners to be on-site during an investigation
major crime scene searches
shooting reconstruction
bullet path analyses
trajectory analyses
the examiner's role in this type of response is defined by agency policy
may need to collect, preserve, and document different items for evidence
small items
fired bullets and cartridge cases
unfired ammunition
handguns
mid-sized items
items bearing gunshot residue
rifles and shotguns
bulk ammunition
large items
vehicle parts
safe doors
furniture