Crime scene analysis involves making observations that lead to questions, then using logic and deductive reasoning to reach conclusions. Deductive reasoning assembles evidence to logically deduce an explanation, like concluding a body was moved based on limited blood at the scene. Sound reasoning considers all factors to avoid false conclusions, while suspicious yet objective analysis helps solve crimes.

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