Forensic Science: Fundamentals & Investigations, 2e Chapter 17. All rights Reserved Cengage/NGL/South-Western 2016

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1 1 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

2 Tl Marks By the end f this chapter yu will be able t: 17.1 Describe hw frensic investigatrs analyze evidence frm tls and tl marks t help slve crimes Describe variatins in tl surfaces that culd be used t identify specific tls Cmpare and cntrast the three majr types f tl marks and prvide examples f tls that prduce thse types f marks. 2 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

3 Tl Marks By the end f this chapter yu will be able t: 17.4 Prvide examples f freign materials fund in tl marks, and elabrate n hw this evidence can be used t link a suspect t a crime scene Analyze and prcess a crime scene at which tls were used t cmmit the crime Outline the sequence f prcedures fr phtgraphing, dcumenting, casting, and cllecting evidence frm tls and tl marks. 3 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

4 Tl Marks By the end f this chapter yu will be able t: 17.7 Justify the claim that tl-mark evidence is usually cnsidered circumstantial evidence, supprting yur claim with facts frm the chapter Discuss the rle f technlgy in crime-scene analysis f tls and tl marks Describe the rles f the Scientific Wrking Grups (SWGs) and Organizatin f Scientific Area Cmmittees (OSAC) in the imprvement f evidence reliability. 4 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

5 Vcabulary abrasin mark cutting mark indentatin mark tl mark 5 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

6 Intrductin The surface f a tl leaves distinctive marks when it is frced against anther surface. The impressins made by any tl culd link the tl t a crime scene and ultimately t the tl s wner. Tl marks are circumstantial evidence. 6 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

7 Tls and Crime Scenes Pssessin f a tl cnsistent with ne used in the cmmissin f a crime des nt establish the suspect s presence at the time f the crime. 7 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

8 Indentatin Marks An indentatin mark is an impressin made by a tl when it is pressed against a sfter surface. It is the negative impressin f the tl. 8 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

9 Abrasin Marks Abrasin marks are made when surfaces slide acrss ne anther. The harder surface leaves scratches n the sfter surface. 9 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

10 Cutting Marks Cutting marks are prduced alng the edge f a surface as it is cut. The type f saw blade used t dismember a bdy can be determined by examining the cut surface f the bne. 10 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

11 11 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

12 Tl Surface Characteristics Tls change ver time as they are used repeatedly. Oxidatin, r rusting f tls, as well as uneven sharpening, are additinal characteristics that help distinguish a tl mark. 12 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

13 Tl Mark Evidence Tl evidence includes bth the mark left at the scene and the tl. 13 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

14 Dcumenting the Evidence Phtgraphing tls Phtgraphing tl marks 14 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

15 Casting Impressins 15 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

16 Casting Impressins (cntinued) 16 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

17 Cllecting and Preserving a Sample All tl evidence is cllected and packaged separately and submitted t a labratry fr analysis. If pssible, the bject cntaining the impressin is remved and sent directly t the lab. Infrmatin t be recrded includes: The case number Date Name Signature f the evidence cllectr Descriptin f where and when the evidence was lcated Why the evidence was cllected 17 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

18 Analyzing Tl-Mark Evidence Crime-scene tl marks and suspect tls are never fitted tgether. This may cmprmise the integrity f the evidence. Instead, impressins frm the crime scene and impressins made frm the suspected tl are cmpared. Serial numbers can pssibly reveal the stre where the tl was purchased. 18 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

19 Tl-Mark Identificatin Technlgy The Ames Labratry is building a tl-mark image database and develping an algrithm t statistically analyze the images. A frensic cmparisn micrscpe is used t cmpare tl marks fund at a crime scene with the images f tl marks fund in the database. Anther prject invlves using three-dimensinal characterizatin methds and statistical methds t distinguish tl marks. This technlgy reduces the subjective nature f tl-mark cmparisn. 19 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

20 Tl-Mark Evidence in the Curtrm Whenever pssible, riginal evidence, such as a tl r an actual tl mark, is presented in curt. Casts and magnified images f tl-mark cmparisns are presented at a trial. As tl-mark analysis technlgy cntinues t advance, frensic experts will be even better able t link a tl and its impressin. 20 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

21 Summary Tls have majr and minr surface differences that can help differentiate ne tl s impressin frm anther s. Tl marks are categrized int ne f three categries: indentatin marks, abrasin marks, and cutting marks. The marks made by tls can link a tl t a crime scene and ultimately link the wner f the tl t a crime. 21 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016

22 Summary (cntinued) Tl-mark evidence shuld be phtgraphed, dcumented, cllected, r cast. Advancing technlgy fr distinguishing tl marks is helping frensic experts link tls t tl marks and cnvict criminals. Organizatins such as the Scientific Wrking Grups and Organizatin f Scientific Area Cmmittees are establishing guidelines and prtcls that will imprve evidence reliability. 22 Frensic Science: Fundamentals & Investigatins, 2e Cengage/NGL/Suth-Western 2016