When I design a murder mystery case file, many of my cases are built around elimination. Evidence is used to either eliminate a suspect, location or window of time. Many cases can be solved faster by eliminating every other suspect until you’re only left with one.

Elimination is a very powerful tool in detective reasoning. You can find out a great deal of information in any mystery by eliminating as many possibilities as possible. This guide explains exactly how that process works and how to apply it.

And for a broader overview of the detective reasoning framework this fits into, see our guide on how to think like a detective.

What Is Eliminative Reasoning?

Eliminative reasoning is the process of narrowing down possibilities by systematically ruling out what cannot be true. Instead of trying to build a case to reach the conclusion you have in mind (which may be wrong), you can identify everything that your evidence contradicts until only one viable option remains.

You may remember this famous expression from Sherlock Holmes: “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” Well, this is the core principle behind elimination. It’s a process of subtraction that eventually leads you the correct answer.

It also helps to move you away from confirmation bias. When you think you already know the answer, you’ll tend to look for evidence that supports your idea. When you work backward, using elimination, you’re forced to look at every piece of evidence.

Deductive vs. Eliminative Reasoning – What’s the Difference?

These two main types of reasoning approaches that are often confused:

Deductive reasoning starts from an established idea and works toward a specific conclusion. For example: if everyone at a party had access to a weapon, and only one person has no alibi during the time of the murder, that person will become the primary suspect. So, you’re reasoning forward using known facts.

Eliminative reasoning works in reverse. You start with all possible suspects – or all possible explanations – and remove each one that the evidence contradicts. So, you’d look at each piece of evidence individually and remove each suspect on-at-a-time until only person remains.

In practice, experienced detectives and skilled mystery solvers use both. Deduction is used to help you test specific theories that you have. Elimination reduces the number of suspects that you’ll need to create theories for. The two methods work together.

How to Apply the Process of Elimination to a Suspect List

The process of elimination will help you solve any mystery much more accurately. Here is how to use it properly.

Step 1 – List Every Possible Suspect

Do not pre-filter suspects on a whim. Write down everyone who could conceivably have committed the crime. Cops often leave out suspects due to first impressions and simply going with people that appear to be hiding something. Everyone needs to be part of your suspect pool.

Step 2 – Work Out Your Elimination Criteria

Before you start ruling people out, work out what would definitively eliminate a suspect. This is usually something like a verifiable alibi, or proof that they were somewhere else, but there can be additional options according to your case.

The motive, means and opportunity framework works great for eliminating suspects. A suspect who doesn’t have any motive, means or opportunity to commit the crime, can quickly be eliminated. A suspect who has all three will stay on the list until new evidence is found.

Step 3 – Work Through the Evidence Methodically

Take each piece of evidence and ask yourself: who does this rule out? Evidence can both point toward one suspect, as well as eliminate another. For example, a large shoeprint can point toward multiple people with large feet, and also exclude a large number of other suspects.

Step 4 – Document What You’ve Ruled Out and Why

You’ll want to keep close track of why each suspect has eliminated. Clearly write down your reason in your file. If later evidence begins to contradict your current evidence, such a lying alibi or someone intentionally wearing oversized shoes – you can quickly add that suspect back.

Step 5 – Re-evaluate When New Evidence is Found

Elimination is not a one-time process. Sometimes investigators get stuck and can’t move their investigation forward. It’s important that you put any new evidence against people that have been eliminated as well. People lie and sometimes a new bit of evidence can lead you to figuring this out, meaning that you’ll need to reinstate a suspect.

So, why eliminate a suspect in the first place if you’re still going to need to need to run evidence against them? Well, you might start out with 20 suspects and eliminate 15 of them for a variety of reasons. A new bit of evidence might have zero connection to most of the eliminated people on your list, but could potentially be linked to just one person. That’s why keeping clear notes of why someone has been eliminated is so important.

Another reason to re-evaluate suspects is when your case goes cold. Most cases are straightforward and eliminating suspects will get you to the correct person faster. However, let’s say you eliminate a few suspects as they weren’t in the country during the time of the murder. You continue investigating, but never track down the right person. You would then need to consider that someone was paid for the murder. In this case, anyone that was eliminated for being out the country would become suspects again, as you’d want to look into their financials to see if they paid someone.

Common Elimination Mistakes

Even the best investigators make these mistakes sometimes.

Eliminating a suspect too quickly. Ruling out a suspect because of a first impression, a feeling, or something they’ve said (without any evidence to back it up) – often eliminates good leads. You need solid proof to before eliminating anyone.

Not revisiting eliminated suspects. While many cases are cut-and-dry, the few that aren’t will require you to take a second look at people that have been eliminated. If any new evidence pops up that changes the circumstances of the case, you’ll always need to take a second look at people that have eliminated from your suspect list.

Treating unlikely as impossible. Elimination should used to rule out what cannot be true – not things that just seem unlikely. If there’s still a possibility that someone could be involved, but it seems unlikely, they can be moved to the bottom of your suspect list – but not eliminated completely.

Eliminating suspects to protect your favorite theory. This is something that’s often done by bad cops. Once they’ve decided what they think happened, they’ll eliminate everyone else from their suspect list and focus all of their attention on just one person. This is the story behind of countless false imprisonment documentaries.

The Elimination Matrix

An easy way of eliminating suspects is to put them onto a matrix.

List every suspect on one axis, and their motive, means and opportunity on a separate axis. Using the evidence you currently have on hand, you can easily eliminate a lot of suspects. If someone has no motive, means or opportunity = they can almost always be eliminated. Even if the culprit paid for someone else to commit a crime, they would need a motive for it.

There are exceptions to every rule, and you’ll eventually come to a tricky case that will have a psychopath or sociopath where no motive is needed, but for the majority of cases, the elimination matrix will work very well.

When playing a murder mystery dinner party game with a group of people, this type of matrix is even more helpful. Everyone gets to pool the information and clues they’ve gleamed from the evidence and from chatting and put it forward to help find motives, means and opportunities. It’s why murder mystery team building works so well as a collaborative exercise.

Elimination in Murder Mystery Case Files

The best-designed mystery case files always have a few suspects to start with and require you to whittle them down. It’s basically elimination puzzles with a good story attached. If you understand this, it makes most cases a lot easier to solve. At the first objective, you’ll generally have 4 or 5 potential suspects, but as you complete each objective, 1 or 2 suspects will be eliminated using the evidence provided.

If you want to put the skills you’ve just learned to work, our collection of murder mystery logic puzzles is a good place to start – as the elimination method worth great with all of them. For a wider range of solo and group options, the best detective games to play at home has many more options to challenge you.

Frequently Asked Questions

What is the process of elimination in detective work?

This is when you systematically rule out suspects, scenarios and explanations using the evidence you have on-hand. It requires investigators to look at every piece of evidence they have and not just cherry-pick evidence that supports their theories.

Is elimination the same as deduction?

They’re related but different.

Deduction is when you start with something you already know is true and figure out what must follow. For example: The killer must have been inside of the house because the murder weapon was found in a locked room that only the guests could enter.

Elimination is the removal of possibilities until only one likely answer is left. For example: Sarah was out of town, Mark had no access to the room, and Lisa has a solid alibi. That leaves only two possible suspects.

What eliminates a suspect in an investigation?

A verifiable alibi that places a suspect somewhere else at the time of the crime is the best reason for elimination (this is called “opportunity“). Besides that, evidence that they lacked the means – the physical capability, the access, the relevant knowledge – or had no conceivable motive also works toward elimination. These all need to proven and you should never just take the word of the suspect.

Can an eliminated suspect be brought back?

Yes, absolutely. An elimination is only ever as good as the evidence backing it. If the alibi that cleared a suspect is later shown to have lied, a witness account is changed, or new evidence is found – the elimination should be reversed. Keeping a record of why each suspect was eliminated – not just who was eliminated – makes this process more manageable.

How does elimination work in murder mystery case files?

Modern cases are split into multiple objectives. As you solve each objective, you’ll automatically eliminate potential suspects. Sometimes, these eliminations are made clear to you through the text, but often, it’s left up to you to keep track of who could, or couldn’t, have committed the crime. By the final objective, you should have a personal list of who you’ve eliminated, leaving only one person as the culprit.

The Simplest Rule in Investigation

If you take one thing from this guide, it’s this: elimination is way more reliable than accusation. You’re far less likely to name the wrong person if you’ve properly ruled out every other possibility first. Your final conclusion isn’t a shot in the dark. It’s a good theory based on evidence, after every other option has been eliminated.

For a full breakdown of the reasoning that detectives use, head over to our main guide on how to think like a detective. And when you’re ready to test your new skills on some fun cases, check out our murder mystery case files to solve at home.