Planning an effective internal investigation after a serious incident

Welcome back to our 2026 monthly series: “Responding to a safety incident – and beyond.” To help you navigate emerging questions and to guide discussion within your organisation, each month we are providing you with practical advice on responding to a safety incident. This month we consider: Planning an effective internal investigation after a serious incident.

When a serious incident occurs, an internal investigation is often essential. Done well, it can help you understand what happened, meet regulatory expectations, support those affected, and reduce future risk. Done poorly, it can create confusion, delay, and unintended exposure. This article sets out the key principles for running an effective internal investigation.

1. Start with a clear purpose and scope

There is often pressure to act quickly, but process should follow purpose. The first step is to agree why the investigation is being carried out and what it will (and will not) cover.

Key scoping decisions include:

• The issues the investigation will focus on
• The time period under review
• Which documents, systems and sites will be examined
• Who will be interviewed
• Early legal input can be valuable – not only to consider legal privilege (see below), but also to help manage how the internal investigation interacts with any regulatory, police or other external investigations running in parallel.

2. Capture facts first – avoid premature conclusions

• Most internal investigations are designed to establish what happened. This often involves building a clear factual timeline: events leading up to the incident, what occurred, and the immediate consequences.
• While organisations are understandably keen to identify causes, there is a real risk in speculating too early. Proximate causes, root causes and contributory factors may not be clear at the outset. For this reason, many investigations initially focus on fact‑finding, deferring evaluative conclusions until the evidence base is secure and better considered.

3. Resource the investigation properly

• Internal investigations are often more time‑ and resource‑intensive than expected. Under‑resourcing can lead to gaps, delays or weak outputs.
• A small investigation team is usually preferable, combining:
  • People who understand the organisation, systems and records
  • Individuals with sufficient independence from the incident itself
  • Where needed, technical or specialist expertise

4. Follow a structured process

• Where investigation procedures already exist, they should be followed. Where they do not, structure is still critical.
• Investigations frequently involve:
  • Large volumes of documents and data
  • Physical evidence
  • Multiple witnesses
  • Parallel evidence requests from regulators or police
• Simple project management tools – such as an investigation plan, document log and action tracker can make a significant difference to control, consistency and defensibility.

5. Secure senior approval and independence

• Senior‑level authorisation (for example from the Board or Executive) is often essential. It provides:
  • Clear authority for the investigation
  • Faster access to documents, systems and people
  • Support for appropriate independence
  • This “buy‑in” can be crucial where cooperation across departments is required.

6. Do not overlook the human impact

• At the centre of most serious incidents are people — injured individuals, bereaved families, affected colleagues and wider communities.
• Those most impacted are often key witnesses. A planned, sensitive approach is therefore essential, including:
  • Appropriate welfare and support
  • Careful sequencing and conduct of interviews
• This helps balance the need to capture accurate evidence with the risk of re‑traumatisation.

7. Understand the value – and limits – of legal privilege

• Legal privilege can protect certain investigation materials from disclosure, but it is not automatic and must be handled carefully.

In summary: effective internal investigations are purposeful, fact‑focused, well‑resourced, structured, humane and legally informed. Getting these fundamentals right early can make a decisive difference when scrutiny is at its highest.