Eugene Liscio, Adam Hayden, & James Moody
Abstract: The use of the laser scanner for documentation at crime and collision scenes has grown significantly over the past ten years. Many law enforcement agencies and private firms who have traditionally used hand measurements or total stations have migrated over to the laser scanner because of the speed, ease of use, and amount of data it can capture. Unlike the total station, the laser scanner requires post processing to align all the separate scans. Depending on the method chosen, differences in accuracy may be noted. However, the use of external references such as spheres or checkerboard targets allows for a robust registration of scan data. Rather few studies have been published that look at the differences in accuracies between laser scanners and total stations. Therefore, this study looks to make a comparison between 20 distance measurements obtained by each instrument at a small to medium outdoor “scene”. The data obtained shows that, on average, the laser scanner and total station provide measurements that are within 0.8 mm of each other with a standard deviation of 2 mm. In one instance there was a maximum difference of 6 mm while in three cases the measurement errors were 0.000 mm.
Frank S. DeRonja, MS Engr & Max Holland
Abstract: Following the 1963 assassination of President Kennedy, the Warren Commission established that one of the three shots fired in Dealey Plaza missed. By 1979, subsequent investigations determined that the first shot fired was the one that missed. Left unanswered was why the first shot missed and how to explain phenomena associated exclusively with the first shot. A traffic signal assembly, under which the presidential vehicle traveled, could have obstructed the first shot but was never technically examined. Beginning in 2010, this assembly was subjected to a number of forensic examinations, including rifle test firings on exemplars. From these findings, it is concluded that the most reasonable explanation for why Lee Harvey Oswald’s first shot missed is that the bullet struck the mast arm of the signal light and was redirected on its flight path, eventually to a concrete curb where the FBI found evidence of a bullet impact.
Gary W. Graff
Abstract: Case management is organizing evidence to be workable, retrievable, and understandable in the context of the scene, providing the foundational and structural framework for crime scene reconstruction (CSR). The importance of proper organization to reconstruction cannot be overstated and has been recognized in the past by pioneers in the field. Organizational efforts should begin at the onset of an investigation with a mindset towards later reconstruction. The author provides an illustrated methodology for organizing case information within a flexible framework that facilitates later identification, retrieval, correlation and analysis. The approach builds upon and expands common evidence documentation techniques, and allows for later inclusion of all types of forensic analysis. The result is a more thorough and comprehensive reconstruction in which supporting documentation is easy to reference and retrieve.
Ross M. Gardner
Abstract: Crime scene analysis is a discipline involving the identification and correlation of various actions that occur during a given incident. These correlations exist as both causal and temporal relationships between the various objects involved in the incident. Although the beliefs that guide crime scene reconstruction are relatively simple and very much a product of common sense, this paper outlines the underlying foundation of these beliefs in detail.
Accuracy and Repeatability of the Laser Scanner and Total Station for Crime and Accident Scene Documentation
David Dustin & Eugene Liscio, P. Eng.
Abstract: The need for quick and versatile scene documentation tools continues to be of great importance at both crime and accident scenes. What was once documented by hand has transitioned to the total station and, most recently, the laser scanner due to its ease of use and capacity to quickly document millions of data points for a more complete documentation of the scene. Both the laser scanner and total station have been accepted in courts all over the world and are in use at police agencies globally. However, few studies, if any, exist that look at the accuracy and repeatability of these laser-based instruments in practice. Therefore, this validation study shows that under controlled conditions for an indoor scene with an expanse of approximately 60 m, the total station exhibited a mean absolute error of 1.1 mm. The laser scanner had similar results using a targeted and targetless registration approach and exhibited mean absolute errors of 1.3 and 1.0 mm, respectively, under the same environmental conditions. All three tests performed for each setup/instrument showed an average standard deviation below 0.5mm. For most crime and accident scene documentation purposes, these results are well within acceptable ranges. Depending on the type of environment, object surface properties, number of scans, distance being measured, choice of setup parameters and other factors, these accuracy values may vary.