An account is at its most complete and least contaminated the first time it is given, and it is never that complete again. Everything done in the first few minutes either preserves it or damages it permanently.
Before a single question.
- Say who you are, what the conversation is for, and what will happen to what they say. A person who does not know why they are being asked answers a question they have invented for themselves.
- Say that they may stop, take a break, or decline to answer.
- Establish that you are there to find out what happened, not to confirm something you already believe.
The free account. Ask them to tell you what happened, from wherever they want to start, and then stop talking. Do not interrupt, do not correct the order, do not ask for a date in the middle of a sentence. Silence is a tool; people fill it with detail, and an interviewer who fills it first has taken that detail away.
Then, and only then, questions.
- Open, not closed: Tell me… Describe… Explain… A question answerable with yes or no returns one bit of information and suggests which bit you want.
- Never a leading question. "Was the car red?" puts a red car into the memory of a person who is trying to help you, and it stays there.
- One thing at a time. Two questions in one sentence get one answer and you will not know which.
- Ask for the words they used. "You said he was big — big compared to what?" Their vocabulary is evidence; yours is not.
The things that destroy an account.
- Do not tell a witness what another witness said. Two accounts that agree because one was told the other are one account, and the case is weaker than if you had never asked.
- Do not show a photograph or a suspect before a description is recorded. Once a face has been seen it cannot be unseen, and any identification afterwards carries the picture you showed.
- Do not express approval or disappointment at what is said. People adjust towards the reaction they get.
- Record as close to verbatim as you can, and note where you are paraphrasing.
Source. Principles on Effective Interviewing for Investigations and Information Gathering — the Méndez Principles — https://interviewingprinciples.com/ and UNODC, https://www.unodc.org/
What this is not. The association is not a police force and this is not an interviewing qualification. Interviewing is a trained skill assessed by watching somebody do it. Where the procedure of your service or the law of your country differs from this page, they govern and this page does not.