Forensic Science: Fingerprints, DNA, and Evidence
Using clues to make evidence-based conclusions
Forensic Science: Fingerprints, DNA, and Evidence
Using clues to make evidence-based conclusions
Science - Grade 6-8
- 1
A detective finds a fingerprint on a glass. The print has many ridges that enter from one side, curve around, and leave from the same side. Which basic fingerprint pattern is this most likely: loop, whorl, or arch? Explain your choice.
A loop looks like ridges that turn back instead of crossing all the way through.
The fingerprint is most likely a loop because the ridges enter from one side, curve around, and leave from the same side. - 2
A fingerprint found at a scene matches a suspect's fingerprint at 12 ridge characteristics. Does this prove the suspect committed the crime? Explain why or why not.
It does not prove the suspect committed the crime by itself. It shows that the suspect may have touched the object, but investigators need more evidence to connect the suspect to the crime. - 3
A DNA sample from a crime scene matches a suspect's DNA profile at several tested locations. What does this tell investigators, and what should they be careful not to assume?
DNA can sometimes be transferred before, during, or after an event.
The match tells investigators that the suspect could be the source of the DNA sample. They should not assume guilt without considering how the DNA got there and whether other evidence supports the conclusion. - 4
Look at the DNA banding patterns. Crime scene DNA has bands at positions 1, 3, 4, and 6. Suspect A has bands at 1, 2, 4, and 6. Suspect B has bands at 1, 3, 4, and 6. Suspect C has bands at 2, 3, 5, and 6. Which suspect's DNA pattern matches the crime scene sample?
Compare each band position one at a time.
Suspect B's DNA pattern matches the crime scene sample because both have bands at positions 1, 3, 4, and 6. - 5
A student says, "Hair found at a scene always identifies exactly one person." Explain why this statement is not scientifically accurate.
The statement is not accurate because hair can provide helpful information, such as color or structure, but it may not identify exactly one person unless useful DNA evidence is present. - 6
At a scene, investigators collect a muddy shoeprint near a broken window. Name two observations they could make from the shoeprint and explain how each observation might help the investigation.
Think about size, shape, tread pattern, and direction of movement.
Investigators could observe the shoe size, which may help narrow down possible suspects. They could also observe the tread pattern, which may help match the print to a type of shoe or a specific shoe. - 7
Why should investigators photograph evidence before moving it?
Investigators should photograph evidence before moving it because photos record the original location and condition of the evidence. This helps preserve information about the scene. - 8
A white powder is found on a table. A student wants to smell it closely to identify it. Explain why this is unsafe and describe a safer scientific approach.
Unknown substances should be treated as potentially dangerous.
Smelling an unknown powder closely is unsafe because it could be harmful or toxic. A safer approach is to leave it in place, wear proper protective equipment, and have trained investigators test it using approved methods. - 9
Investigators collect a small piece of broken glass from a suspect's jacket. They also collect glass from a broken window. What properties could scientists compare to see whether the glass pieces may have come from the same source?
Scientists could compare properties such as color, thickness, density, and how the glass breaks or bends light. Similar properties may support the idea that the pieces came from the same source. - 10
What is chain of custody, and why is it important in forensic science?
Think of it as a tracking record for evidence.
Chain of custody is the record of who collected, handled, stored, and tested evidence. It is important because it helps show that the evidence was not lost, changed, or contaminated. - 11
A fingerprint is found on a door handle at a busy school office. Why might this fingerprint be less useful than a fingerprint found on a locked cabinet inside the office?
The fingerprint on the door handle may be less useful because many people could have touched it for normal reasons. A fingerprint on a locked cabinet may be more important because fewer people would be expected to touch it. - 12
A crime scene has three clues: a partial fingerprint on a drawer, a shoeprint in mud, and a DNA sample on a cup. Explain why using all three clues together is stronger than using only one clue.
Strong conclusions are usually supported by more than one piece of evidence.
Using all three clues together is stronger because different types of evidence can support or challenge the same conclusion. A fingerprint, shoeprint, and DNA sample together can give investigators a more complete picture than one clue alone.