Laser Ablation Inductively Coupled Plasma Mass Spectrometry of Forensic Glass Samples
David Baldwin, Sam Houk, and Stan Bajic, Ames Laboratory
Characterization of glass fragments is normally accomplished by measuring the physical and optical properties of density and refractive index. However further discrimination, such as identification of a suspected source of origin, has become more difficult as the range of refractive indices has narrowed within glass subtypes because of advances in glass manufacturing technology. This project proposes to evaluate laser ablation-inductively coupled plasma-mass spectrometry in order to determine the unique trace elemental signature or fingerprint of glass samples, and to develop criteria and protocols for the comparison and differentiation of glass fragments from different sources.
Alloy Assessment of Firearms Related to Acid Etching Forensic Techniques
Dave Utrata, Iowa State University
This work would correlate the alloy analysis of various firearms to optimized forensic etching techniques used for the recovery of obliterated serial numbers. This recovery is facilitated by the selection on the most suitable etchant for any given firearm, based on an awareness of the alloy used. Beyond a superficial knowledge of properties of the samples, investigators typically are forced to experiment with an array of etchants, singularly or in sequence. This work will use a portable tool to generate a list of firearm alloy analysis, thereby guiding a criminologist to select the right etchant for a given firearm.
Development of Magnetic Particle Method for Forensic Recovery of Serial Numbers
Dave Utrata and Marcus Johnson, Iowa State University
This work will generate guidelines and insight for the proper use of the magnetic particle method as a forensic tool for the recovery of obliterated serial numbers on ferrous samples. Practitioners of this method for nondestructive inspection are well aware that a successful inspection will be the result of using a magnetic field of appropriate magnitude and orientation, the correct nature of the magnetizing current (AC/DC/rectified) and a suitable choice of magnetic particle suspension. Investigators in crime labs currently use this method in a manner that provides only sporadic success at best. It is timely to remedy this situation.
Development of a Magnetic Imaging Technique for Nondestructive Restoration of Serial Numbers
M.J. Johnson and C.C.H. Lo, Iowa State University
Conventional techniques for restoring obliterated serial numbers are partially destructive. Nondestructive alternatives are sought as they will allow the subsequent application of other methods to the test piece and do not destroy evidence in criminal cases. We propose a method based on an array of high-resolution, high-sensitivity Hall or GMR sensor elements. The array probe will be used to image the stray field that results from residual plastically deformed regions, the remains of the imprinted serial numbers. Successful implementation of the proposed technique will provide an efficient, nondestructive forensics tool for recovering obliterated serial numbers without the need for surface preparation or other processing.
Quantitative Characterization of Machining Marks for Comparative Identification
L.S. Chumbley, Ames Laboratory, and L. Genalo, Iowa State University
This project seeks to provide law enforcement officials with quantitative data concerning the nature of tool affected surfaces. The work will involve examination of surfaces using a combination of optical microscopy coupled with quantitative measurements of the surface relief. The surface will be examined optically and regions of interest identified for replication using a simple technique. The resulting replica will be characterized using a two-dimensional profilometer. The data will be statistically evaluated to ensure that the replica accurately portrays the surface and, if so, attempts will be made to identify an unknown sample by comparison to known samples. If successful, this process should yield a forensic technique that is rapid, easy to perform, and applicable to any shaped surface.