1. THE CRIME SCENE

1. 1. THE CRIME SCENE • It is the responsibility of the first officer on the scene to take steps to preserve and protect the area to the greatest possible extent.

2. First – get medical attention if needed. • Second – exclude all unauthorized personnel • Third – isolate the area

3. Fourth - Record the scene. This is very important because it may be necessary to present it in court. The three most common methods of recording the scene are :

4. Photograph, Sketches, and Notes • Photographs can be digital or SLR type or video tape.

5. Photographs should include many different angles, close-ups, and surroundings. • Rough sketches can be made at the scene and include an accurate depiction of the dimensions of the scene.

6. From a rough sketch a more detailed sketch called a finished sketch is derived. Often a CAD program is used to make a 3-dimensional view of the scene.

7. Notes should include a detailed written description of the scene with the location of items of physical evidence.

8. Notes must be very accurate because they may be the only way to recall the scene in months or years.

9. Fifth - Conducting a Systematic Search for Evidence. • The type and area of the search will be determined by the location and size of the area, the actions of the suspects, and the actions of the victims.

10. Physical evidence may be collected using vacuums. • The body of the victim must also be examined for physical evidence.

11. These include scrapings from under the fingernails, the victims clothing, hair, blood, recovered weapons or bullets, and hand swabs from shooting victims for gunshot residue analysis.

12. Sixth - Maintain Chain of Custody • Continuity of possession, or chain of custody, must be established whenever evidence is presented in court as an exhibit.

13. This means every person who handled the evidence must be accounted for. Failure to keep a clear chain of evidence can lead to questions regarding its authenticity and integrity.

14. 2. Legal Considerations of the Court Evidence must be collected with care so as to fulfill the legal requirements of the courts.

15. *The problem usually arises from an illegal search without a warrant. • *Conditions where a warrant-less search can be conducted include:

16. *The existence of emergency circumstances. • *The need to prevent the immediate loss or destruction of evidence.

17. *A search of a person or property provided it is followed by an arrest. • *A search made by consent of the parties involved.

18. Outside of these parameters a warrant should be obtained to ensure evidence collected will be admissible in court.

19. 3. Common types of physical evidence: • Human and animal body fluids including objects which may contain residue such as clothing and cigarette butts.

20. Documents • Drugs • Explosives, including items that have residue on them • Fibers (types?) • Fingerprints

21. Firearms and ammunition • glass and glass fragments • Hair • Impressions such as tire marks, shoe prints, bite marks

22. Paint that may have been transferred • Petroleum products which could indicate arson • Powder residue from firearm discharge

23. Serial numbers which can be used to identify items. • Soil and minerals imbedded in shoe or fabric

24. Tool marks – any impression made by a tool used in the commission of a crime. • Wood and other plant matter found on an object or person linked to the crime

27. 4. The Significance of Physical Evidence • A. Identification has as its purpose the determination of a substance with as near absolute certainty as possible.

28. Examples: • Identify the chemical composition of drugs such as heroin, cocaine, etc. • Identify residue from fires and explosions such as gasoline or dynamite.

29. Identify bodily fluids, hair, or plant matter including identification of species.

30. B. Comparison is the process of ascertaining whether two or more objects have a common origin.

31. Examples: • Comparing hair found at a crime scene and hair removed from a suspects head. • Paint on a hit-and-run victim and paint on a suspects car.

32. Evidence that can be associated with a common source with an extremely high degree of probability is said to posses individual characteristics.

33. For example, Victor Balthazard has mathematically determined that the probability of two individuals having the same fingerprint is 1 X 1060!

34. 1,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000, 000,000 to 1

35. C. Class Characteristics • Often a piece of physical evidence does not meet the criteria for individual characteristics. Sometimes it can only be associated with a single source.

36. This evidence is said to have class characteristics. Probability is the key factor between the two. • Ex. Paint chips from a car v. paint chips from a car that has been painted three times.

37. Ex. Blood: two specimens, both human, both type A. • About 36% of the population has type A. Could they have a similar origin?

38. When other factors ( EsD1 and PGM 2+2) occurring in blood are also taken into consideration the probability of matching them to a common source increases. This is called the product rule.

39. Product Rule – Multiplying together the frequencies of independently occurring genetic markers to obtain an overall frequency of occurrence for a genetic profile.

40. Physical evidence may also be used to exclude or exonerate a person form suspicion. • Ex. If a type A blood is linked to a suspect, all individuals with type B, AB, or O can be eliminated from suspicion.

42. When does evidence stop becoming class and start becoming individual? • Not clear, so it is important for the forensic scientist to find as many characteristics as possible when comparing one substance with another.

43. 5. Crime-scene Reconstruction. • Reconstruction is the method used to support a likely sequence of events by observation and evaluation of physical evidence, as well as statements made by those involved with the incident.

44. Even though the reconstruction alone does not describe everything that happened at a crime scene, it can support or contradict accounts given by witnesses or suspects.

45. It can also generate new leads. • As evidence is collected everything must be recorded with photographs, sketches, and notes.

46. By carefully collecting evidence and documenting the crime scene, scientists can put in order the sequence of events that took place in the commission of a crime.

47. Things that can be revealed by a reconstruction. • Information from the way a body is found. Its position relative to its surroundings.

48. Has the body been moved? • Bullet paths and shooter positions. • Blood spatter analysis. • Locating gunshot residue deposited on a victims clothing can indicate the distance from a shooter to the target.

49. Properly done, crime-scene reconstruction can be a valuable tool in aiding a jury in determining the appropriate verdict.

50. Physical and Chemical Properties Properties can be divided into 2 broad categories, physical and chemical.