UNIT 3: Types of Physical Evidence Textbook Chapter 2 (Forensic Science for High School)

Transcription

1 UNIT 3: Types f Physical Evidence Textbk Chapter 2 (Frensic Science fr High Schl) Unit Vcabulary: Evidence: Testimnial Evidence: Physical Evidence: Indirect Evidence: Circumstantial Evidence: Questined r Unknwn Sample (Q): Knwn Sample(K): Cntrl Sample: Individual Evidence: Class Evidence:

2 Lcard s Exchange Principle EVERY CONTACT LEAVES A TRACE The value f trace (r cntact) frensic evidence was first recgnized by in He was the directr f the very first crime labratry in existence, lcated in Lyn, France. The Lcard s Exchange Principle states that "." Fr example, burglars will leave traces f their presence behind and will als take traces with them. They may leave hairs frm their bdy r fibers frm their clthing behind and they may take carpet fibers away with them. Individual vs. Class Evidence Material that can be related t a single surce; individualizatin always invlves a cmparisn Material that can be assciated nly with a grup f items that share prperties r characteristics Physical and chemical analysis f paint evidence (chips r residue) can indicate it s, such as autmbile paint, huse paint, nail plish, etc. The evidence can be t different types f paint classified in a database, which can be used t identify a particular make r mdel f car r brand f tl. Paint evidence can als indicate characteristics if an investigatr is able t find similarities between, such as the clr, number f layers, chemical cmpsitin, r a physical match between the edges f tw paint chips ne frm a tl and ne frm a crime scene. DID YOU KNOW: Mst paint evidence submitted t a lab will cme frm hit-and-run cases invlving autmbiles. Glass particles can be fund at varius crime scenes, such as. Glass at a crime scene is analyzed t determine its clr, surface characteristics, tint, thickness, density, chemical cmpsitin, and refractive index (RI). The results f the tests prvide clues abut the crime and help investigatrs cnnect the evidence t a suspect r

3 ther bject used in a crime, such as matching glass frm a crime scene t a headlight t a suspect s car. Explsive substances can be examined t determine its t identify the type f explsive used and its rigin. f explsives fund n a suspect s clthing, skin, hair, r ther bjects may be matched t explsives frm the crime scene. Materials used t make an explsive device will be cmpared t evidence fund in the suspect s pssessin t cnfirm a match. Characteristics f ammunitin, firearms, and residue are examined t find matches between suspects and the evidence fund at a crime scene. Chemical tests can reveal n the hands, face, r clthing f a victim r suspect t indicate hw clse a persn was t a fired gun. DID YOU KNOW: Caliber (handguns & rifles) r gauge (shtguns) refers t the size f the internal diameter f a gun s barrel. Rifling (grves) in a gun barrel causes distinctive grves, indentatins and scratches upn fired bullets, which can be matched t the weapn that fired them. Plice are able t search database t cmpare markings frm bullets, cartridge cases, and shtgun shells t ballistic evidence. Dust, dirt, r sand evidence can reveal where a persn has and may be picked up at a crime scene r left behind. Investigatrs examine the samples fr chemical cmpsitin, pllen, plant material, and ther rganic matter t find links t a specific crime scene. There are 3 types f fingerprint patterns:. Investigatrs als identify unique ridge characteristics in a fingerprint that can be used t identify a suspect r victim. is a database used by investigatrs at lcal, state, and natinal levels t search fr matches t fingerprints fund at a crime scene.

4 Impressin evidence can be phtgraphed, with tape, r with plaster t cmpare t a suspect s shes r tires. Investigatrs will examine the evidence t identify the brand f r based n its tread pattern and ther physical features t prvide leads in the case. Shes and tires will als shw after being used fr a perid f time as well as ther features (scratches, nicks, and cuts) that can be used t match evidence t specific items. Fr example, sheprints can be matched t a suspect based n hw the treads n the shes that are wrn dwn due t that persn s. Each f the teeth in humans is unique due t age and wear. Impressins and phtgraphs f bite marks left n a victim, assailant, r ther bject at a crime scene can ften be matched t. Tiny frm n the edges f a tl as it is used, which can be used t identify matches between evidence and suspects. Tls may als pick up traces f bld r ther substances that can be tested r have fingerprints that can be lifted. When an bject brken, trn, r cut, tw unique edges are frmed, which are referred t as. These edges can be by the naked eye r with micrscpes t see if they fit tgether, which indicates that they may have been part f the same bject at ne time. Investigatrs may cmpare the edges n pieces f tape, glass fragments, paint chips, pieces f a car frm an accident, paper bag, etc. t find pssible matches. Wunds can ften be matched t weapns r tl marks n the weapn. Investigatrs may als be able t determine the weapn's size, shape, and length. Analysis f a wund may prvide clues t a victim s injuries, f the suspect (left-handed, right-handed, height, etc.), and f the victim and suspect at the time f the incident.

5 Examiners will analyze a r ther dcument t find clues t link it t a crime scene r a specific suspect. They will analyze the type f paper used, printing methd r handwriting style, and type f ink. Other unique features, such as watermarks n statinary r made as smene wrte n a page in a ntebk, may prvide useful clues. Flies, beetles, and ther insects can prvide useful clues abut a. Frensic entmlgists use factrs such as, the lcatin and cnditin f the bdy, and their knwledge f the life cycles f insects t help them estimate the pstmrtem interval r (the time between death and the discvery f the bdy). Investigatrs can extract frm almst any tissue, including hair, fingernails, bnes, teeth and bdy fluids. The DNA is used t create a that can be cmpared t prfiles frm suspects r victims. (Cmbined DNA Index System) is a database maintained by the FBI that is used t find matches t unknwn DNA samples frm a crime scene. Frensic anthrplgists analyze t determine fur characteristics fr a victim: age, sex, race, and stature (height/build). - Determined by examining the pelvis, humerus, and femur Determined by analyzing the develpment f the teeth, bne grwth, and the length f specific bnes, such as the femur. Determined by analyzing the skull fr characteristics that are cmmn amng peple f different races. DNA samples can be cllected frm bne, teeth, and hair t prvide clues t a persn s identity. Scientists may als be able t gain clues as t a persn s past, recent, r the cause f death based n bne fractures and ther signs f trauma.

6 What d frensic anthrplgists d? Generally, frensic anthrplgists DO NOT d any f the fllwing: trace evidence (hair, fibers) Run DNA tests Analyze ballistics r evidence Analyze spatter Cnduct autpsies What a frensic anthrplgist des DO t aid in a case: Ges t a crime scene t assist in the cllectin f Cleans up the s that they may be lked at Analyzes skeletal remains t establish the f the individual Lks at evident n the bnes t establish the pathway f a bullet r the number f stab wunds Wrks with a frensic (dentist) t match dental recrds Testifies in curt abut the identity f the individual and/r the injuries that might be evident in the skeletn Bld, semen, saliva, sweat, and urine can be analyzed t give investigatrs infrmatin abut the crime as well as its victim r the suspect. can be used at a crime scene t find bdy fluid evidence. Areas with ptential evidence are swabbed, bagged and cllected in vials, which are and have a lw risk f crss cntaminatin. Examples: Vmit and urine can be used t test fr alchl, drugs, and pisns. Cigarette butts may cntain dried saliva. Semen cntaining sperm is valuable fr DNA analysis. Bld can prvide DNA evidence and bld spatter can prvide clues abut the crime. Hairs and fibers may be frm the suspect r the suspect s clthes t the victims and vice versa. Fr example, a suspect may pick up carpet fibers n his shes r leave hairs behind at a crime scene. Hairs can be examined t identify their, such as human r animal. Hairs with rts intact can be tested fr DNA. Fibers are used t make clthing, carpeting, furniture, beds, and blankets. They may be natural fibers frm plants r animals r synthetic fibers that are man-made.