Case rethinking: a protocol for reviewing criminal investigations

Abstract

Mistakes in decision-making have been identified as the most common type of error in police investigations. Consequently, wrongful convictions and other types of criminal investigative failure may require a complete case ‘rethinking,’ particularly when new evidence disrupts the existing theory. A rush to judgment resulting in a premature shift from an evidence-based to a suspect-based investigation can produce a number of problematic thinking errors. Faulty assumptions, tunnel vision, groupthink, and other cognitive biases and organizational traps hinder evidentiary interpretation and evaluation. This article outlines a protocol for reviewing evidence and rethinking a wrongful conviction or unsolved crime when the existing investigative theory appears to be incorrect. The protocol involves four stages: (1) evidence; (2) interpretation; (3) patterns; and (4) analysis.

Keywords:

• criminal investigation
• police detectives
• criminal investigative failures
• cold cases
• wrongful convictions

Acknowledgements

I wish to thank Dr David Stubbins, Central Intelligence Agency (ret.), Deputy Chief Constable Doug LePard, Vancouver Police Department, Detective James Trainum, DC Metropolitan Police Department (ret.), Special Agent Gregg McCrary, Federal Bureau of Investigation (ret.), and the anonymous reviewers for their helpful comments and suggestions.

Notes

1. This is similar to moving from an evidence-based to a suspect-based investigation (Rossmo, 2009), or from information generation to case building (Stelfox & Pease, 2005).

2. A study on bias in criminal investigations found participants who were asked to identify a suspect early in the process showed a greater tendency to confirm that hypothesis, and later ‘remembered’ the case evidence as being consistent with their particular suspect’s guilt (O’Brien, 2009).

3. Police investigators rarely test their theories by searching for disconfirming evidence even though it is more probative than confirmative evidence (e.g., exclusionary DNA). Once a narrative of the crime has been adopted, police tend to focus only on gathering confirmatory evidence (Stubbins & Stubbins, 2009).

4. Templates for reviewing major crimes and evaluating cold cases have been previously proposed (e.g., Adcock & Stein, 2013; Jones, Grieve, & Milne, 2008b). The present protocol differs from these tools in its focus on how to rethink a case.

5. It may not be feasible to reanalyze every item of evidence in an investigation. The goal is to list all the nontrivial items that might have an influence on the theory of the crime and its suspects. Trivial, however, does not mean inconsistent or contradictory.

6. Reliability is used here to refer to the accuracy or ‘truthfulness’ of evidence, consistent with most of the legal literature. However, the correct scientific term is validity.

7. Heuer’s (1999) analysis of competing hypotheses matrix can be a useful tool here.

8. The probability of evidence given a theory is not equal to the probability of the theory given the evidence; confusing cause given effect with effect given cause is known as the prosecutor’s fallacy (Robertson & Vignaux, 1995). Bayes’ theorem provides the mathematical relationship between the two probabilities (Taroni, Aitken, Garbolino, & Biedermann, 2006).