1. Deductive reasoning and logic
Making connections

2. How crime scene analysis works
• The first step to crime scene analysis is making
observations.
• Observations lead to questions…or…problem
statements.
• Example: What crime was committed?
Who committed this crime?
How was this crime committed?

3. Using logic
Logic: a system of reasoning and
inferences (conclusions that
are based on observations)
• In context of forensics: does
the evidence and the
description make sense?

4. • Example: A body was found in an alley.
The body had multiple stab wounds but
there is very little blood at the crime
scene.
• What is one logical explanation/inference
of the crime that you can make with this
information?

5. Deductive reasoning
Deductive reasoning: A
thought process that
investigators use to
assemble the pieces
of a criminal puzzle to
reach a logical
conclusion.

6. Looking at facts
(AN example of deductive reasoning)
• Facts:
– Ice cream sales go down in the winter
– Statistics show that there are fewer instances
of domestic violence in the winter
• Facts:
– Ice cream sales go up in the summer
– Statistics show that there are more instances
of domestic violence in the summer

7. What is the logical link?
• When ice cream sales go
up domestic violence
goes up.
• When ice cream sales go
down domestic violence
goes down.
• Conclusion: The more ice
cream that is sold, the
more domestic violence
there will be…the less ice
cream sold the less
domestic violence

8. Cause and effect
• Describe the cause and effect of ice
cream and domestic violence…
• If ice cream sales stop then domestic
violence will also stop.
• Do the two really go together?

9. • While it may seem
like the two go
together, it does not
mean that ice cream
sales really effect
domestic violence

10. • What we see when we look at the facts is
a relationship that really doesn’t exist
because we are only seeing a part of the
whole picture…leading to misinterpretation
• What are some other pieces of the puzzle
that we haven’t seen yet?

11. Reasoning
• False reasoning, as
we just saw, can lead
to errors and
misunderstandings or
misinterpretation
when evaluating
evidence and results.

12. Sound reasoning
• As experts with a lot of
experience, many
forensic scientists use a
combination of suspicion
and reasoning to help
solve crimes.
• Using sound reasoning
allows for valuable
interpretation of evidence
while still maintaining
objectivity