Workplace Investigation Process: Step by Step

A workplace complaint has landed on your desk. Now what? If you get the investigation wrong, you've wasted time, upset employees, and created evidence that works against you if it goes to tribunal.

Here's exactly how to do it right.

What Is a Workplace Investigation?

A workplace investigation is a formal process to establish facts when there's a complaint or allegation: bullying, harassment, theft, breach of confidentiality, performance issues, or conduct concerns. It's separate from the disciplinary decision. You investigate to find facts. Later, you decide what to do about them.

Most investigations take 2–6 weeks depending on complexity.

Before You Start: Three Key Decisions

Who will investigate? If you're close to the situation, or if the complaint is about your direct report, get someone else to investigate. It looks fairer and it is fairer. If you investigate and it goes to tribunal, a judge will ask why you didn't use someone independent. Answer: fairness.

What exactly are you investigating? Be specific. "Bob's performance" is vague. "Bob has missed three deadlines in September, causing delays on Project X" is specific. Write down the allegations clearly before you start. This is your terms of reference.

Who needs to know? Keep the complaint confidential. Only people who need to know (the person you're investigating, their manager, HR) should be told. If you gossip about it, you look unprofessional and you create bias.

Step 1: Plan the Investigation

Write down:

• What you're investigating (the specific allegations)

• Why (what's happened, who complained, when)

• Who will be interviewed (the complainant, the accused, witnesses)

• Timescale (how long it will take)

• Confidentiality (remind everyone to keep it quiet)

Don't deviate from this plan once you've started. It keeps you fair.

Step 2: Inform the Accused

Tell the person being investigated, in writing, what's being alleged. They need to know so they can prepare their response. If you investigate them without telling them what's alleged, it's not fair.

Include:

• The allegations, clearly stated

• When they'll be interviewed

• That they can bring a companion

• Confidentiality reminder

• The investigation timeline

Give them at least 5 working days before the interview.

Step 3: Interview the Complainant

Interview the person who raised the complaint first. Get their full account, in writing or recorded (recorded is better if they're happy with it).

Ask:

• What happened (specific incidents, dates, times)

• Who witnessed it (names of people who saw or heard)

• What impact it's had on them

• Whether they've told anyone else

• What outcome they want

Don't judge or jump to conclusions. Just listen and document.

Step 4: Interview Witnesses

Interview anyone who was present or who the complainant or accused mentioned. Interview them separately. Interview the accused's version of events from their perspective too.

Key rules:

• Interview separately (never together)

• Use consistent questions across all witnesses

• Don't lead ("didn't he shout at you?") — ask open questions ("what happened?")

• Document everything: names, dates, times, what was said

• Get them to sign or confirm the notes are accurate

• Remind them of confidentiality

Step 5: Interview the Accused

Interview the person being investigated. Tell them:

• The specific allegations

• What witnesses have said (don't name them if that would compromise safety)

• Ask for their account of events

• Give them time to respond to what's been alleged

• Listen without interrupting

• Don't make a judgment on the spot

Document everything, just as you did with other interviews.

Step 6: Gather Documentary Evidence

Collect emails, messages, records, policies, shift patterns — anything that's relevant. If something's digital, take a screenshot and date it (digital evidence disappears).

Step 7: Analyse and Write Findings

Review all the evidence. For each allegation, decide: Is it proven, on the balance of probabilities? (This is the civil standard: more likely than not, not "beyond a reasonable doubt".)

Write a report that includes:

• What you investigated (terms of reference)

• Who you interviewed

• A summary of what each person said

• The evidence you considered

• Your findings for each allegation (proven or not proven)

• Recommendations (e.g., "Recommend disciplinary hearing" or "No case to answer")

The report should be factual, not emotional. Stick to evidence.

Step 8: Share Findings

Send the investigation report to:

• The accused (so they can respond)

• The complainant (so they know what was found)

Give them 5 working days to comment. They might say "You got this wrong" or "You missed something." Listen to their response.

Step 9: Make a Decision

After you've heard responses, decide what to do. Your options:

• No case to answer (investigation found nothing to substantiate)

• Refer to disciplinary (investigation found allegations were proven)

• Refer to capability (if performance is the issue)

• Refer to mediation (if it's a conflict between two people)

• Other action (training, reshuffle, etc.)

The investigator doesn't make this decision. You do (or a disciplinary panel does). The investigator's job is to find facts.

Step 10: Communicate the Outcome

Tell both parties the outcome, in writing. Explain:

• Whether allegations were proven

• What action you're taking (if any)

• Their right to appeal

• That retaliation is not acceptable (important: people sometimes face blowback after an investigation)

Common Mistakes in Workplace Investigations

Investigating while angry. You've just heard an allegation and immediately start asking people about it. You're biased and it shows.

Only talking to one side. If you only interview the complainant and the accused, you've missed witnesses who might change the picture.

Asking leading questions. "Didn't he treat you unfairly?" leads them to say yes. Ask "How did he treat you?" instead.

Making a decision during the investigation. "I don't believe him" isn't a finding. "Based on the evidence, I find this allegation was/was not proven" is.

Not documenting. If it's not written down, it didn't happen. Write notes during interviews or immediately after.

Taking too long. More than 6 weeks is unfair on everyone. Get it done.

Not keeping it confidential. If everyone knows about it, you've compromised fairness and the quality of evidence.

Red Flags That Your Investigation Won't Hold Up

• No interview notes

• Only one person interviewed

• No documentary evidence attached

• The investigator is friends with the accused

• No written record of what was alleged

• The complainant is never told what was found

• The accused isn't given a chance to respond to the allegations

Any of these will weaken your case if it goes further.

Timeline Guide

• Days 1–2: Plan the investigation

• Days 3–5: Inform the accused

• Days 6–8: Interview complainant and initial witnesses

• Days 9–12: Interview other witnesses and the accused

• Days 13–20: Gather evidence, analyse findings, write report

• Days 21–25: Share report, get responses

• Days 26–28: Make decision, communicate outcome

Total: 4 weeks. Complex investigations might take 6–8 weeks.

The Bottom Line

A fair investigation is documented, thorough, and separate from the decision. It takes time, but it's fairer on everyone and it protects you legally.

Do it right and even if the outcome upsets someone, they can't say you didn't listen or weren't fair.

Need help with a workplace investigation? We conduct fair, independent investigations for bullying, harassment, performance concerns, and complex allegations.