csi'/ forensics fingerprint identification

ForensicsIdentification of Fingerprints

• No 2 people have the same fingerprints

• Fingerprints can solve crimes.

• Fingerprints are impressions created by ridges on the skin.

• Ridges form before a baby is born and maintain their pattern throughout life.

• As you grow, the pattern gets larger, but does not change.

Fingerprints

2 layers of skin

• Dermis, the deepest layer which contains sweat glands, oil glands, nerves, and blood bessels.

• Epidermis, made of several layers of cells that are arranged along ridge patterns.– Outter-most cells of the

epidermis are dead and they dry out and fall off.

Latent Prints

• When a person touches an object, the perspiration, oils, and amino acids on his or her skin are transferred to that object. Sometimes an impression of the ridge pattern is left in the deposit.

• Fingerprint—the impression left• Prints are not usually visible to the naked eye,

so they are called latent (hidden) prints.

Classification of fingerprints

• Fingerprints have general patterns of ridges that allow them to be classified and compared. All fingerprints are divided into three large groups, based on their ridge pattern.

Loop• Loops are found in 65% of the population

Whirl

• Whorls are found in 35% of the population

Arch• Arches are found in 5% of the population

Which is it?

Which is it?

Basic and composite ridge characteristics

ridge ending bridge

Bifurcation double bifurcation

dottrifurcation

island (short ridge) opposed bifurcations

lake (enclosure) ridge crossing

hook (spur) opposed bifurcation/ridge ending

Mini Lab #1: Identifying our

Fingerprints

• Pass out worksheet

Identify your prints

• Classification and Ridge characteristics

Identify LATENT prints

• Latent prints (hidden) must be located and preserved. There are two basic techniques for finding fingerprints. – 1. Dusting– 2. Chemically fixing

Fingerprint Dusting

• Hard surfaces such as glass and tile yield prints when lightly dusted with powder.

• Fingerprint powders come in a variety of colors so that the investigator can always apply one that will contrast with the surface holding the print. The powders can be brushed in place with either a camel-hair or fiberglass brush.

Chemical fixing• Chemicals can be used to help find

fingerprints on many types of smooth surfaces.

• Forensic specialists may use chemicals to reveal prints and then take pictures of them– Super Glue fuming produces good prints on

nonporous surfaces such as a metal, leather, and plastic. In this technique, Super Glue is heated in an enclosed area that contains the evidence in question. Prints appear in an off white shade.

CSI Fingerprint Lab, Part II

Pointing out Perpetrators Lab• When Mrs. Henley walked into her science class,

she was surprised by a birthday cake topped with an incredible number of candles. Students broke into an off key rendition of “Happy Birthday” and gave her a standing ovation.

• “For the first time, I’m speechless”, Mrs. Henley said. “I can’t believe you guys prepared this birthday surprise for me. Do you really think I need all these candles? Before we eat, tell me who brought the cake, dishes, forks, napkins, and drinks? I want to thank you personally.”

• No one spoke as Mrs. Henley looked around the room, waiting for a response. “What’s the matter? Are you bashful? Who brought all of this good stuff?”

• Still the students smiled and remained silent. Mrs. Henley was amused, and decided to make the best of the situation. “OK. Lets try something. The birthday party conspirators moved some glass slides from the table to set up the cake. I think we can use these slides to identify our modest hosts.”

Super Glue Fuming

• Aquarium with light bulb and super glue set up.

• Fingerprint ID on all students/ worksheet using graphite.

• ID conspirators prints along with whether they have a loop, whorl or arch.

• Determine the % of loops, whorls, and arches in the class for the Data Table.