1. Latent Prints
Forensic Science
T. Trimpe

2. REVIEW VIDEO: Watch the video on the
How to compare fingerprints:

3. What are latent fingerprints?
Latent fingerprints are invisible.
Fingerprints are formed from material on the fingers that is pressed upon a surface.

4. What causes latent prints?
Oils secreted by the fingers
Sweat on the pores on the skin
Proteins from the surface of the skin

5. Things that affect oil or sweat can leave bad prints
What kind of things do you think would affect oil?

6. Are all surfaces likely to have latent prints?
Hard and nonabsorbent surfaces
Easy: Glass, glossy tile, porcelain, lacquered furniture, smooth metal.
Involved: Paper, painted surfaces, drywall, cardboard, leather, most dashboards.
Difficult: Organic surfaces (tree leaves, fruit peels, feathers) or treated surfaces.

7. How can we see latent prints?
There are 6 basic methods.
We will cover 3 of them:
Print powders
Superglue fuming
Silver nitrate

8. Some investigators use fluorescent powder and UV lights to help them find latent prints on multi-colored or dark surfaces.
Magnetic powder can also be used to reveal latent prints. This type of powder works better on shiny surfaces or plastic baggies or containers.
The cyanoacrylate fuming method (often called the super glue method) is a procedure that is used to develop latent fingerprints on a variety of objects.
Ninhydrin is a chemical that bonds with the amino acids in fingerprints and will produce a blue or purple color. It is used to lift prints from surfaces such as paper and cardboard.
Top Left:
Bottom Left:
Bottom Right:

9. Lifting latent prints with powders
Powders stick to the oils left behind on fingerprints
Different powders are used for different surfaces

10. Black powder, basically charcoal, is applied to white or light colored surfaces.

11. If the video does work by clicking on it then follow the link to watch on Youtube

12. Types of powders...
Gray powder, aluminum dust, is used on dark surfaces. It is also applied to mirrors and metal surfaces.

13. Fluorescent powders are also used to develop latent fingerprints
Fluorescent powders are also used to develop latent fingerprints. These powders light up under UV light.

14. Directions:
1 - Cover your table with white butcher paper or newspaper. You must dust everything on the paper!
2 - Get a lifting kit from your teacher that contains powder, brushes, and clear tape.
3 - Press the pad of your right thumb on a glass slide/ or tile to make a print. Place on the paper covering your table.
4 – Dip a brush lightly into the container of powder and then tap off the extra on the lid. You only need a very small amount of powder to dust the print.
5 – Hold the brush over the print and rotate it between your thumb and fingers. Use the brush to remove any extra powder.
6 - Use a small piece of clear tape to lift the print and place it in the box on your worksheet.
CAUTION: The black powder will be messy and isn’t easy to clean up. Don’t dust anything without permission!

15. Clean Up
1 – Clean off the slides/tiles and put them back in the kit with the brushes and tape.
2 – Have someone help you fold the paper in half and tap it to return the extra powder into the container.
3 – Put the powder in the box and have it checked in by your teacher.
4 – Get a towel and “dry” wash the table – especially the edges that weren’t covered with paper.
5 – Get a wet towel to wash off the table and then wipe it with some dry towels. Keep cleaning until all the powder is off the table!

16. Super glue fuming method
Super glue is placed on tray with the evidence.
The fumes are then created by heating the glue.

17. Fumes from the glue stick to the latent print, usually producing a white colored latent print.

18. Watch the video on the cyanoacrylate fuming method (often called the super glue method):

19. Silver nitrate method
Silver nitrate works well on porous surfaces like paper or fabric.
Based on the reaction of silver nitrate with the salt and proteins in fingerprints.

20. It is very good on old fingerprints when the other methods usually fail.
Only use it after trying the other methods, as it will destroy the print.

21. How to use the silver nitrate method...

22. REVIEW GAME Follow the link to play the review game.
BE SURE TO READ ALL THE INSTRUCTIONS CAREFULLY BEFORE PLAYING THE GAME.
THIS IS REVIEW… NOT A RACE!
Take your time!
YOU MUST RAISE YOUR HAND TO SIGNAL THE TEACHER OVER TO CHECK ONCE YOU HAVE CORRECTLY IDENTIFIED ALL 12 FINGER PRINTS!