Caught Red Handed!

Name: ______________________________________________________________________________________________ Period: ____________________
Caught Red Handed!
In this lab you will learn about how law enforcement uses scientific principles to solve crimes based on
fingerprint data.
Why Fingerprints?
The two fundamental principles of fingerprint identification are that fingerprints are permanent and unique:
fingerprints never change and no two fingerprints are the same.
Fingerprints are formed before birth, and while they grow larger throughout a person’s life, their basic structure
remains constant. They can be temporarily obscured when the skin is damaged; but once healed, the ridges grow
back in the exact same pattern. Even when a fingerprint is permanently scarred, there is almost always sufficient
detail around the scar to allow for a positive identification. Uniqueness
Fingerprints are made up of skin ridges - or friction ridges - that have unique pattern formations. Examiners are
able to evaluate and compare the flow or ridges, the relationship between ridge endings and other details to make
an identification. Beside being unique in fingerprints, ridge detail is also unique in the palms of hands and the soles
of feet.
Fingerprints vs. DNA
Both fingerprint identification and DNA analysis have proved to be valuable tools for personal and criminal
identification. However, fingerprint identification can be more accurate than DNA analysis. Even identical twins
that look exactly alike and have the same DNA structure will always have different fingerprints! This is because
fingerprints are formed in the womb, where movements and natural growth randomly create the characteristics.
1. Describe the process that forms your fingerprint design. Is this trait something that is coded for in your
2. Is fingerprint design an inherited or acquired trait? Explain your answer.
3. Do you think each one of your fingerprints has the same fingerprint? Why or why not?
4. Keep your hands about a foot from your face and look at your fingerprints. Can you tell the design on your
fingerprints? Does each fingerprint look the same, or different?
5. Still keeping your hands about a foot away from your face, compare your fingerprints to the fingerprints of
your neighbor. Can you see any differences?
Now, we are going to look more closely at your fingerprints. You will be making darker copies of your fingerprints
using pencil lead. But first….let’s make some predictions! Write a hypothesis using the if…then…. format for each
1. Will each of your fingerprints look the same? (If I make a clear, dark copy of each of my fingerprints,
2. Will your fingerprints look the same as your neighbors?
1. Rub lead on a piece of scratch paper. Make your lead mark big enough to fit your whole fingerprint.
2. Rub your fingerprint in the lead mark on your scratch paper.
3. Take a piece of clear tape at least 1.5 inches long and put it on your finger over the lead.
4. Press the tape firmly onto your fingerprint.
5. Take the tape off, and put it on the specified table in this packet. Make sure you put each finger in the
correct box.
6. Repeat this process for all 5 fingers on ONE of your hands.
1. Were your hypotheses correct? Make sure to address each of your two hypotheses.
Forensic scientists are trained to look for specific, identifiable patterns in your fingerprints. Using these patterns,
they can classify fingerprints based on their physical characteristics. Using the classification chart below and the
hand lenses at your table, identify the pattern in each of your fingerprints. Write your answer on the table next to
each fingerprint.
1. Why is it important for forensic scientists to look closely when making observations?
2. How does this relate to some of the scientific principles we have learned in class this year? Do any other
areas in science require us to look very closely (perhaps even microscopically)? List and describe as many
as you can. You must have at least five, but the person who thinks of the most examples will win a prize!