1. Police officers’ use of evidence in suspect interviews: How and Why?
Serra tekin, PÄr Anders Granhag & Leif A. StrÖmwall
/06/2016

2. Imagine… A woman has been murdered
The crime took place between 1 am and 2.30 am on a Sunday morning
A suspect was arrested
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3. Victim’s Facebook page
Suspect is home, calls a friend
(3 am)
Victim’s Facebook page
(2 days before)
Suspect calls the friend again
(4.15 am)
Party
(night of the murder)
1 am
2.30 am
Before
Murder
After
Evidence exists
No evidence
Evidence exists
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4. The investigators possess evidence pertaining to several (less critical) phases of the crime, but lack information about the most critical phase
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5. How should the suspect be interviewed to elicit information about the critical phase (between 1 am and 2.30 am)?

6. Research questions
How do investigators use the available evidence when their aim is to elicit admissions about the critical phase? Why?
Investigators’ planned evidence use
Investigators’ reasoning behind their planning
/06/2016

7. Method: Survey
N = 69 police officers (fictitious case + questions regarding planning) The Netherlands (n = 50, 72%) Norway (n = 15, 22%) U. K. (n = 4, 6%) Age: 24 to 59 (Myears = 42.1, SD = 9.3) Experience: 1 to 28 years (M = 9.9, SD = 6.8) 66% received training on suspect interviewing
/06/2016

8. Case & objective
Objective: You are now asked to plan an interview with the suspect based on the case information. In this interview, your objective is to collect new information from the suspect. Specifically, we would like you to focus on eliciting new information to be able to infer whether there is any link between the suspect and the crime scene
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9. The piece of information
Column 1
Column 2
Column 3
The piece of information
What question would you ask related to this piece of information?
What do you want to achieve with your question?
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10. The piece of information
Column 1
Column 2
Column 3
The piece of information
What question would you ask related to this piece of information?
What do you want to achieve with your question?
The victim was killed with several blows to the head
How did you kill Linda?
Figure out how the crime has taken place and more importantly why.
Suspect’s route leaving party
The suspect was on the phone at night
What is your calling behaviour?
To check whether he calls more often at night
The red sweater
Where do you spend your income on? How much money do you spend on your hobbies? How much money do you spend on clothes? What kind of clothes do you like? What kind of clothes do you wear? What clothes did you wear to the party?
He cannot later say it was someone else who had his sweater
CCTV footage
Suspect’s browser history
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11. Coding- Planned use of evidence
Strategic (obtaining the suspect’s statement before disclosing a particular piece of evidence)
Column 1
Column 2
Column 3
The piece of information
What question would you ask related to this piece of information?
What do you want to achieve with your question?
Eyewitness statement indicating that the suspect was drunk at the party
Can you tell me what you have drank at the party?
/06/2016

12. Coding- Planned use of evidence
Non-strategic (disclosing the evidence to the suspect before posing questions about it)
Column 1
Column 2
Column 3
The piece of information
What question would you ask related to this piece of information?
What do you want to achieve with your question?
Eyewitness statement indicating that the suspect was drunk at the party
We have eyewitness evidence indicating that you were drunk at the party. Tell me what you have drank
/06/2016

13. Results- Planned Use of Evidence
283 questions were formulated (+ 37 were in the ‘other’ category) Strategic use: 70% of the time Non-strategic use: 30% of the time The investigators planned to use the evidence strategically (M = 2.87, SD = 2.42) more often than non-strategically (M = 1.23, SD = 1.67) .
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14. Results- Planned Use of Evidence
N = 69 investigators, 3 groups of investigators
31 (44.9%): planned to disclose all pieces strategically
12 (17.4%): planned to disclose all pieces non- strategically
26 (37.7%): planned to disclose some pieces strategically, others non-strategically
/06/2016

15. Coding- Reasoning behind Planning
7 categories
1- To obtain new information about the evidence already held
2- To compare the suspect’s statement with the evidence already held
3- To encircle
4- To obtain new information about the critical phase of the crime
5 To obtain new information about a theme unrelated to the crime
6- To support a hypothesis
7- Other
Column 3
What do you want to achieve with your question?
To clarify why the suspect made two phone calls very late at night
/06/2016

16. Coding- Reasoning behind Planning
7 categories 1- To obtain new information about the evidence already held 2- To compare the suspect’s statement with the evidence already held 3- To encircle 4- To obtain new information about the critical phase of the crime 5- To obtain new information about a theme unrelated to the crime 6- To support a hypothesis 7- Other
Column 3
What do you want to achieve with your question?
To compare the suspect’s statement about the chain of events with the witness statements
/06/2016

17. Coding- Reasoning behind Planning
7 categories
1- To obtain new information about the evidence already held
2- To compare the suspect’s statement with the evidence already held
3- To encircle
4- To obtain new information about the critical phase of the crime
5-To obtain new information about a theme unrelated to the crime
6-To support a hypothesis
7-Other
Column 3
What do you want to achieve with your question?
To establish who else uses the phone
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18. Coding- Reasoning behind Planning
7 categories 1- To obtain new information about the evidence already held 2- To compare the suspect’s statement with the evidence already held 3- To encircle 4- To obtain new information about the critical phase of the crime 5- To obtain new information about a theme unrelated to the crime 6- To support a hypothesis 7- Other
Column 3
What do you want to achieve with your question?
To find out the suspect’s route from the party to his home
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19. Results- Reasoning behind Planning
 Categories
 Strategic Use of
Evidence
% (n)
 Non-strategic Use of Evidence
1. To obtain new information about the evidence already held
22.3 (47)
43.4 (36)
2. To compare the suspect’s statement with the evidence already held
35.5 (75)
13.3 (11)
3. To encircle
12.8 (27)
1.2 (1)
4. To obtain new information about the critical phase of the crime
9.5 (20)
6.0 (5)
5. To obtain new information about a theme unrelated to the crime
6. To support a hypothesis
6.6 (14)
24.1 (20)
7. Other
3.8 (8)
10.8 (9)
/06/2016

20. Results- Reasoning behind Planning
 Categories
 Strategic Use of
Evidence
% (n)
 Non-strategic Use of Evidence
1. To obtain new information about the evidence already held
22.3 (47)
43.4 (36)
2.  To compare the suspect’s statement with the evidence already held
35.5 (75)
13.3 (11)
3. To encircle
12.8 (27)
1.2 (1)
4. To obtain new information about the critical phase of the crime
9.5 (20)
6.0 (5)
5. To obtain new information about a theme unrelated to the crime
6. To support a hypothesis
6.6 (14)
24.1 (20)
7. Other
3.8 (8)
10.8 (9)
/06/2016

21. The notion of… …using the known information (pertaining to less critical phases) as a vehicle to elicit admissions about a phase for which information is lacking IS RATHER NOVEL
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