The Crime Scene

1. The Crime Scene

2. Physical Evidence and the Crime Scene • Physical Evidence – any object that can establish that a crime has been committed or can link a crime and its victim or its perpetrator.

3. Preserving and Recording the Crime Scene • Secure and Isolate the Crime Scene. • The responsibility of the first responding officer. • Priority is medical assistance to any individuals in need and arrest of any perpetrator.

4. Record the Scene      A.  Photography - The scene should be unaltered - Objects that have been moved or removed must not be replaced - Objects should be photographed showing their position and location relative to the entire scene.        -Crime-scene photographers usually          use cameras with 12 megapixels or               more.

5. B. Sketches Rough Sketch – A sketch drawn at the crime scene, that contains an accurate depiction of the dimensions of the scene and shows the location of all objects having a bearing on the case.

6. Finished Sketch - A precise rendering of the crime scene, usually drawn to scale. - Finished sketches are often done with CAD (computer-aided drafting) software.

7. Notes - Must be constant throughout - Must include a detailed written description of the scene with the location of items of physical evidence recovered. - Must identify the time an item of physical evidence was discovered as well as who and how it was collected.

8. Dealing with Physical Evidence • There are specific procedures for finding, collecting, and transporting physical evidence. • Conduct a Systematic Search for Evidence - How a crime scene is searched is dependent on the locale and size of the area as well as the actions of the suspect(s) and victim(s) at the scene.

10. Collect Physical Evidence - Can be anything from very tiny to very large. - Clothing from all persons present at a crime scene may be necessary. - Critical areas should be vacuumed and the sweepings submitted to the laboratory for examination.

11. Efforts should be made to avoid changing evidence in any way. • Each different item or similar items collected at different locations must be placed in separate containers. Packaging evidence separately prevents damage through contact and prevents cross-contamination.

12. Forceps may be used to pick up small items. • Packaging materials may include plastic pill bottles, manila envelopes, and plastic bags. • If the materials are too small for the container, a paper bindle (AKA Druggist Fold) may be used to keep the specimen contained. • Wet items must not be packaged in airtight containers as they may grow mold which contains its own DNA.

13. Fire evidence must be placed in an airtight unbreakable container to prevent the evaporation of volatile petroleum residues.

14. Maintain the Chain of Custody Chain of Custody– a list of all people who came into possession of an item of evidence. - As all of the individuals involved in the collection and transportation of evidence may be required to testify in court, this should be kept to a minimum.

15. D.  Obtain Standard/reference sample • Physical evidence whose origin is known, such as blood or hair from a suspect, that can be compared to crime-scene evidence. • One example of a reference sample would be a buccal swab.

16. Buccal Swab - a swab of the inner portion of the cheek performed to collect cells for use in determining the DNA profile of an individual.

17. Substrate control - uncontaminated surface material close to an area where physical evidence has been deposited; used to ensure that the surface on which a sample has been deposited does not interfere with laboratory tests. 

18. Proper standard/reference samples, such as hairs, blood, and fibers must be collected at the crime scene and from appropriate subjects for comparison purposes in the laboratory.