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Achieving best evidence from witnesses in investigations



Most employers, from time to time, face complex investigations in the workplace which sees them interviewing different categories of witnesses. This could be, for example, children or young people, those with certain disabilities, witnesses who are reluctant to give evidence or who are intimidated, those who are hostile to the process or an accused person facing very serious accusations. It could also be the case that the sensitive nature of what is being investigated by an employer means that a more careful and sensitive approach needs to be adopted by an investigator.

In our previous briefings, we have discussed the importance of getting workplace investigations right. In this briefing, we will look at the correct style of interviewing certain types of witnesses in the context of workplace investigations. 

We all know that witnesses are the key to many types of investigation and that unlocking all of the relevant evidence can turn the course of an investigation. So, how can we achieve best evidence? Helpfully, there are lessons, research and good practice that we can draw from the criminal justice system to improve the quality of interviews and in turn investigations.

In the criminal justice system, practitioners, lawyers and the judiciary use particular frameworks for different groups of witnesses. Suspects in criminal cases are interviewed under the PACE codes (ie Police and Criminal Evidence Act 1984 (PACE)). A separate framework, “Achieving Best Evidence" (ABE) is guidance from the MOJ, intended for use in criminal proceedings, to interview two categories of witnesses which we will focus on in this note.

Vulnerable witnesses and intimidated witnesses

Vulnerable witnesses are:

  • Children (ie all those under 18).

  • Those who have a mental disorder as defined by Mental Health Act 2007.

  • Witnesses who have a learning disability.

  • Witnesses who have a physical disability but only if the quality of evidence given is likely to be diminished by reason of the disability.

Intimidated witnesses are:

People whose quality of evidence may be diminished by reason of fear or distress. Factors to take into account:

  • Nature and circumstances of the alleged offence.

  • Age of the witness.

  • Where relevant: social, cultural background and ethnic origin, religious beliefs or political opinion.

  • Also relevant could be behaviour of the accused, their family or associates.

In the criminal sphere, complainants in cases of sexual assault fall into this category as do witnesses to other specific crimes such as victims and witnesses of domestic violence, racially motivated crime, crime motivated by reasons relating to religion, homophobic crime, gang related violence, those who are elderly and frail.

Whilst we know our employer clients are not interviewing witnesses for the purposes of the criminal justice system, it is the case that they will encounter victims of (or witnesses to), for example, harassment, discrimination, extreme bullying all of which have adverse impacts on witnesses and can be traumatic.

ABE provides for special measures in the criminal system to make the process for these witnesses more robust and therefore reliable with the aim of the interview process being less distressing so that they can give their best evidence. If implemented properly, a great deal of time, care and planning goes into an ABE interview. 

Can employers and investigators use the principles of ABE to improve the quality of interviews in workplace investigations?

Yes and there are lots of reasons to want to do this. Poor quality interviews can lead to:

  • Poor quality investigations overall.

  • Incorrect conclusions being drawn.

  • Key evidence being missed.

  • Wrong or unfair decisions in later proceedings.

  • Referrals to agencies/regulators not being made (when they should be) or conversely being made when they shouldn’t be.

  • Complaints or even grievances about the process.

  • Adverse findings against employers in the tribunals.

So, how can the ABE principles be used?

Below are some examples.

Planning for an interview is key. Thinking about the witness:

Everyone is different. What does the investigator need to know about this witness to get their best evidence? This could include:

  • Medical/health issues that they would need to know about.

  • First language and cognitive ability.

  • Ability to sequence events.

  • Age, gender/gender identity, preferred form of address.

  • How can the witness prepare? Will they get a chance to practice interview questions using a neutral topic?

  • How will the interviewer introduce themselves to the witness?

  • Does a “truth and lies” exercise need to be done for example with young children?

  • How do I get the topic of concern into the room with this witness without asking leading questions?

  • Is any type of pre-interview assessment needed?

Thinking about the interview

  • Who is best qualified to lead this interview? Do they have experience of interviewing in relation to similar allegations / evidence? Where relevant, do they understand the impact of harassment, discrimination or even trauma?

  • Is there a need for another person to be there such as an interview supporter, interview monitor, interpreter, intermediary?

  • How will the interview be recorded? Digitally recorded or note-taking or both?

  • Do any adjustments need to be made to the room such as lighting, noise / sound or other distracting issues dealt with?

ABE contains a number of checklists starting at page 35 see here.

Ground rules for a robust interview

Most people aren’t used to having to give very detailed descriptions of events and it’s an unusual thing to have to. It may help witnesses to be made aware of certain rules such as:

  • The witness is the expert in this information – the interviewer wasn’t there or involved in what happened.

  • It’s important not to guess, so say the witness should say if they don’t know the answer and only talk about things that have happened.

  • It’s important to correct the interviewer if they get something wrong.

  • It’s the interviewer’s job to help the witness understand the questions, so the interviewer needs to think of the best way to ask the questions.

Investigators and interviewers should be careful because some vulnerable witness have a “yes bias” and are susceptible to suggestibility. This can be countered by careful planning for an interview, structuring the interview properly and asking the right questions.

In an ABE interview a four phased interview approach is set out

Phase 1 is establishing rapport.

Phase 2 is the free narrative account (from the witness).

Phase 3 is questioning (the witness).

Phase 4 is closing.

The best interviews will be conducted with the use of open questions that gives space for the witness to provide their free narrative account, with help from the interviewer with the use of prompt type questions eg:

“tell me more”,

“tell me more about that”,

“describe that”,

“explain that”.

These are called open questions. Research says that this style of questioning is more likely to trigger recall memory which is the most reliable part of the memory in terms of evidence giving. “Open–specific” questions are the next best category of questions eg “describe the man”. An investigator will evitability have to use specific questions during an interview: who, what, when, where but if the whole interview is conducted with specific questions only it will become an exhausting process, so try to go back to the open or open-specific questions. 

Forced choice (“was it pink or blue?”), closed questions that require “yes” or “no” and leading questions (“you were in the cafe at the same time, weren’t you?”) should all be avoided.


In Safeguarding circles, we now hear more about being “trauma-informed” or “taking a trauma-informed approach”. To be trauma-informed means that you:

Understand and identify the symptoms or behaviours of someone who may have suffered trauma.

Understand the impact of trauma on the brain and body. (The charity Mind contains information about trauma, what it is and the impact).

Recognise that treating people with respect, empowering people and ensuring their safety in all processes will help in the person’s recovery from trauma.

Take steps and put in place strategies to avoid retraumatising, which could happen in an interview, particularly if you are interviewing the witness about the event that was traumatic.

There are generally considered to be 5 – 6 key guiding principles to a trauma-informed approach:


Trustworthiness & transparency Peer support

Collaboration & mutuality

Empowerment & choice

Cultural, historical & gender issues

For example, in planning for an interview, we can carefully consider strategies to make sure that the witness feels physically and psychologically safe. Investigators can achieve trustworthiness and transparency when they provide information to the witness in advance and during the interview itself, for example by giving advance notice about the questions that are coming (“I am now going to ask you some questions about what happened after you spoke to Mr Smith”).

Further information on being “trauma-informed” can be found here.

There are many things to think about and lots of different styles of questioning. Reflect on the principles of ABE and always remember to follow other guidance where it is applicable such as ACAS guidance and EHRC guidance as well as the employer’s policies and procedures.

If you require further information about anything covered in this briefing, please contact Maria Strauss, Kathleen Heycock, or your usual contact at the firm on +44 (0)20 3375 7000.

This publication is a general summary of the law. It should not replace legal advice tailored to your specific circumstances.

© Farrer & Co LLP, October 2021

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About the authors

Maria Strauss lawyer photo

Maria Strauss


Maria advises a broad spectrum of clients including private companies, not-for-profit organisations, independent schools, banks, sports clubs, Churches and faith-based organisations on employment law and safeguarding matters.

Maria advises a broad spectrum of clients including private companies, not-for-profit organisations, independent schools, banks, sports clubs, Churches and faith-based organisations on employment law and safeguarding matters.

Email Maria +44 (0)20 3375 7259
Kathleen Heycock lawyer photo

Kathleen Heycock


Kathleen's legal expertise and pragmatic approach is welcomed by both her employer and senior executive clients.  She believes in getting know her clients so that she can ensure they achieve an outcome that meets their immediate objectives and that also fits with their long term professional and personal goals.

Kathleen's legal expertise and pragmatic approach is welcomed by both her employer and senior executive clients.  She believes in getting know her clients so that she can ensure they achieve an outcome that meets their immediate objectives and that also fits with their long term professional and personal goals.

Email Kathleen +44 (0)20 3375 7113

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