Sample Class
INTRO TO FORENSIC SCIENCE
CJT 1000
LESSON OUTLINE – SESSION 3
REVIEW PREVIOUS LESSON
- What are the objectives of crime scene photography?
-What are the three general types of crime scene photographs?
-What are the objectives of a crime scene sketch?
-What “information” should the crime scene sketch contain?
-What is the value of fingerprints?
-What are the three general ridge patterns utilized for fingerprint classification?
-What is the Automated Fingerprint Identification System (AFIS)?
-What is the Integrated Automated Fingerprint Identification System. (IAFIS)?
LESSON OBJECTIVE
This lesson focuses on a very important type of forensic evidence - fingerprints.
Emphasis will be placed on the following:
-Techniques for taking “record” inked fingerprints.
-Identifying fingerprints at a crime scene.
-Techniques for developing latent fingerprints at a crime scene.
FINGERPRINTS
In previous classes we discussed the importance of fingerprints to the investigative process.
-“Record” inked fingerprints. (Once a subject has been arrested record fingerprints are taken. Today we will practice this skill. Refer to the handout and fingerprint card provided. Each student will print a set of record fingerprints belonging to their partner.)
-Practical exercise.
-Latent fingerprints. (What are they? They are impressions transferred to a surface.)
-Patent prints. (Prints that are visible to the naked eye.)
-Transfer. (Positive transfer impression. Blood – grease.)
-Removal. (The visible area is that portion not touched by the friction ridge.)
-Negative. (Impression of the ridge in soft material – clay paint.)
-Plastic prints. (Created when fingers touch against some material such as new paint, wet glue, putty, and clay.)
-Contaminated/visible prints. (Created when the finger is dirty or contaminated with a foreign matter. Blood, ink, soot, facial powder, and oils.)
-Invisible prints. (They are hard to see and result from perspiration and body oils that are normally found on the friction ridges.)
Factors that affect the quality of latent fingerprints.
-Surface.
-Finger pressure. Requires firm but not heavy pressure – otherwise the ridges are flattened.
-Environmental factors.
-Amount of contamination.
-Physical defects.
-Investigative effort.
-ocating latent fingerprints.
-Start your search at the entry point and conduct it in a systematic manner.
-Plastic and visible prints are fairly easy to detect.
-Invisible are a challenge. Consider using a strong flashlight, or a UV light.
-Look in obvious places-put yourself in the position of the criminal.
-Wear gloves.
Developing latent fingerprints.
-The material used is dependent upon the surface the print is found on.
-Powder. The type and color of the powder depends upon the surface the print is found on. The powder adheres to water and fatty deposits. Colors can be white, black, gray, silver and even red. Works best with new prints on smooth nonporous surfaces.
-Practical exercise. Each student will identify and “lift” three latent fingerprints.
-Fluorescent powders. Good on confused backgrounds. Requires the use of a UV or forensic light.
-Practical exercise. Students will identify and lift two latent fingerprints utilizing a forensic light and fluorescent powder.
-Chemicals.
-Iodine fuming. Works well on porous and nonporous surfaces. Iodine is a solid crystal that, when heated, is transformed into a vapor without passing through a liquid phase – sublimation. Need to photograph and fix the print, as it will fade.
-Ninhydrin. Good for paper or cardboard. Spray it on – can take up to ten days to develop. Results in purplish prints.
-DFO. Physical developer. Good for porous surfaces. A form of ninhydrin – requires a blue light.
-Practical exercise. Students will identify two latent fingerprints utilizing Ninhydrin or DFO.
-Superglue Fuming. First used in Japan in 1978 brought to the U.S. by the US Army CID. White color.
-Collection of fingerprints.
-Photograph prior to collecting. (1 on 1 scale.)
-If a plastic print – collect the object that contains the print.
-If in doubt let a professional develop and lift the print.