Common Mistakes Investigators Make — And How to Avoid Them

Introduction

We are all human with strengths and weaknesses. Even experienced investigators fall into predictable traps. Awareness of these pitfalls improves the quality of investigations and protects the integrity of findings.

During my early years as investigator, one assignment in Romania required screening all employees of a production plant after strategic materials had gone missing. Despite thorough controls at the gate, one employee with a questionable background was suspected of extracting components at the end of his shift. To maintain he investigation discrete, we conducted interviews under the pretence of routine psychological evaluations. Naturally, the suspected employee was at the center of our attention. However, written assessments pointed us in an unexpected direction. A high performer with an impeccable background triggered high dissimulation indicators in the CPI test revealing a very different side of the individual than his reputation suggested. What began as a straightforward suspicion quickly turned into a more complex psychological puzzle, illustrating once again that behaviour, stress and deception rarely align with surface level assumptions.

Mistake 1: Jumping to Conclusions

Confirmation bias is one of the most dangerous cognitive errors. Investigators must actively seek disconfirming evidence and remain open to alternative explanations.

Mistake 2: Poor Documentation

Incomplete notes, missing timestamps, and vague summaries weaken the credibility of your evidence. Detailed, documented records are essential for defending your position.

Mistake 3: Overreliance on Closed Questions

Closed questions are excellent in funnelling down a “waffler” to get a YES – NO response. But they also limit the interviewee’s ability to provide context. Openended prompts generate richer, more accurate information and reduce the risk of leading the witness.

Mistake 4: Ignoring Emotional Cues

During interviews, non-verbal and para-verbal cues are even more valuable than the words themselves. Interviewees communicate through tone, posture, and hesitation. Overlooking these signals can cause investigators to miss opportunities for deeper exploration.

Mistake 5: Lack of Preparation

Effective investigations require planning: understanding the case, mapping timelines, and identifying key issues. Preparation ensures interviews are focused and efficient.

Conclusion

Avoiding these common mistakes strengthens investigative outcomes and enhances the professionalism of the process. Continuous improvement through practice is the hallmark of a skilled investigator.