Trace Evidence

Trace Evidence

At a crime scene tiny fragments of physical evidence like hair, fibers, paint, or glass can be obtained. Trace evidence from a crime scene is either gathered directly or indirectly from the clothing of a victim or suspect. As a forensic scientist, you examine the physical, optical and chemical properties of a questioned sample using microscopes and compare those either against known standards or to a reference sample . Such evidence is often used to reconstruct an event and to indicate that a certain person or thing was present at the crime scene.
 

Preliminary examination

A preliminary examination using stereo microscopes provides quick, accurate and generally non-destructive means to characterize trace evidence. Items to examine can vary from adhesive tape, to clothing. In order to identify individual microscopic traces it might be necessary to use different light conditions such as UV or to use special boom stands. You need stable instruments that offer the required flexibility.

Hair examination

You examine if hair is animal or human, from which body part it originates, and if it exhibits racial characteristics. Therefore, you study the inner and outer morphology using transmitted light microscopes. Shape, color, texture and other visual aspects need to be taken into account when you compare hair found at the crime scene with hair of e.g. a suspect. High reproducibility and comparable results are key to your successful examination.
 

Fibers

In the forensic lab fibers are generally classified as natural, synthetic and inorganic. The fiber under investigation is compared with a known sample. Typically, fibers are mounted in special liquids with known index of refraction and are characterized with respect to various parameters such as relative refractive index, color, and morphology. Especially synthetic fibers are examined with polarization contrast in order to characterize the birefringent properties of the material. Fluorescence microscopy or micro-spectrophotometry often complement your examination to determine the spectrum of dyed fibers. Using scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) allows you to visualize the morphological details of the fibers in high resolution and to obtain their chemical composition.

Paint

As a forensic paint examiner you characterize the color, number of layers, layer sequence and thickness of the paint by mainly using light microscopes. For further physical and chemical characterization of a paint chip with FT-IR microscopy, micro-spectrophotometry or SEM with EDS the different layers are generally dissected individually under a stereo or zoom microscope. The data obtained is particularly useful in automotive paint analysis, where databases are used to identify possible brands, models and years of manufacture of motor vehicles.

Recommended Products for Trace Evidence

Axio Zoom.V16

Axio Zoom.V16 is your motorized fluorescence zoom microscope. You profit from a 16x zoom in combination with a high numerical aperture of NA 0.25. This zoom microscope achieves a very high numerical aperture in the medium zoom range already: you get superior fluorescence brightness in large object fields. In addition to brightfield, darkfield and oblique illumination, you get an increased contrast brightfield at the touch of a button. With the Best Mode button, the stereo zoom microscope Axio Zoom.V16 determines the actual optical state and optimizes transmitted light automatically. Save your setting and reload it for your next investigation of trace evidence. You always get reproducible, comparable results.

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Axio Imager 2 for Polarized Light

Axio Imager 2 allows a wide range of applications for forensic analysis and examinations, e.g. failure analysis, gunshot residue, fiber or paint analysis. With the motorized reflector turret, for six or ten Push & Click filter modules, you can easily work with all the different contrast methods in transmitted or reflected light. The pre-centered Bertrand optics allows you to switch easily between orthoscopic and conoscopic observation. Due to the motorization and the automated component recognition (ACR) you can rely on your microscope settings at all times. Save your individual settings and retrieve them effortlessly with a push of a button. Due to the ability to use additional correlative microscopy you can transfer your samples to a ZEISS electron microscope for further investigations.

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ZEISS EVO

EVO

EVO Scanning Electron Microscopes allow capturing topographical details at low voltages with beam deceleration . The high definition backscattered electron imaging in combination with EVOs unique X-ray geometry provides high resolution performances at analytical working conditions. Choose between three different chamber sizes to investigate a wide range of specimen sizes, including large objects in the fields of forensics trace evidence.

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