Four Investigative Lessons from Sherlock Holmes

“One should always look for a possible alternative, and provide against it. It is the first rule of criminal investigation.”

When I read all of the Sherlock Holmes stories for the first time a few years ago, I was surprised at how good the stories were as investigative case studies. 

The stories held up very well in terms of the methods and approaches that Sherlock Holmes used, and they actually provided what I thought were some useful advice for real-life investigations. I’ve shared these lessons with lawyers and law students, and I wanted to share these with you, along with suggestions for how you can apply them in real life cases.

First, Holmes knew how to solve cases because he had studied past cases. 

From a Study in Scarlet: 

“If you have all the details of a thousand misdeeds at your finger ends, it is odd if you can’t unravel the thousand and first.” 

Sherlock Holmes did not approach each murder as if it was the first murder he had encountered.  He studied each in comparison to all the murders that he had studied beforehand.  This way, he could make comparisons and draw contrasts more easily, and he could notice things that others missed.

Similarly, when I get a new case, I compare and contrast it with similar cases that I’ve done before as well as with other cases that I’ve studied or heard about.

In real life, just about any case you may do has been done before, somewhere.  So when you have a case, don’t start from scratch and don’t reinvent the wheel, but see how other people have done similar cases.  Look for news articles about similar cases, and pull the filings from those cases to see how those cases unfolded - not just the end result, but the process that got there. You can even try calling up the people who worked on those cases – you might learn something helpful.

Second, Holmes knew what the baseline was and how the world he’s investigating works. 

A famous exchange from Silver Blaze:

Colonel Ross: “Is there any point to which you would draw my attention?” 

Holmes: “To the curious incident of the dog in the night-time.” 

Colonel Ross: “The dog did nothing in the night time.” 

Holmes: “That was the curious incident.” 

In this story, Holmes was able to eliminate one theory because he knew how the world worked.  No stranger approached the crime scene during the night because the dog would have barked if that had happened.  But the dog had not barked.

Lawsuits and criminal cases are generally about things that went wrong. No one gets charged or sued for a perfectly normal day where everything went right.

This is why it’s important to understand how things are supposed to work normally.  How should things have gone that day, or how did things normally work?  Establish a baseline and make sure that your audience understands the same baseline that you do.  This will make it easier to show how things went wrong and to notice the red flags that might be valuable clues.

Third, Holmes changed his perspective – he put himself in the place of the people he was investigating.

From A Study in Scarlet: 

“What is out of the common is usually a guide rather than a hindrance.  In solving a problem of this sort, the grand thing is to be able to reason backward.”

From the Musgrave Ritual: 

“I put myself in the man’s place and, having first gauged his intelligence, I try to imagine how I should myself have proceeded under the same circumstances.”

If you’re investigating a case, you should shift your perspective and see things from other points of view.  How would the people actually living through the events you’re investigating actually have handled things and discussed things?

Modern cases often involve reviews of massive amounts of emails.  I’ve seen cases where people come up with search terms that are finely tuned to match what they think the case is about, but miss things because people did not talk or email or text using such perfect search terms.  Finding the right emails is not about what is easy for you, but about figuring out how your subjects actually communicated.

When I review emails and text messages, I start off by reviewing a lot of emails to see who my key people communicate with and how they do so.  I think about the circumstances that might lead to the smoking gun emails that I’m trying to find, I test searches, and I revise my searches. 

For example, I’ve found that searching for curse words can be very effective.  People don’t usually email or text using such curse words – when they do, it sometimes is a response to some key event that I can build my case around.

And fourth, Holmes understood that building a real case requires much more than knowing whodunnit.

From the Greek Interpreter: 

“If the art of the detective began and ended in reasoning from an arm-chair, my brother [Mycroft Holmes] would be the greatest criminal agent [investigator] that ever lived.  But he has no ambition and no energy … he was absolutely incapable of working out the practical points which must be gone into before a case could be laid before a judge or jury.” 

Knowing who did it or what happened is not enough in real life. This may be why movies end so often with the bad guys confessing or getting themselves killed in a dramatic fashion - many of those bad guys might not get convicted if they actually went to trial.

Investigators should focus not on what you believe, but on what you can actually prove to a group of complete strangers.  Oftentimes, that means getting more evidence than you think you need, especially because some of the evidence may not work out as well as you’d like.

Investigators should think about the Federal Rules of Evidence and what will actually be admissible in court.  Anonymous information can provide great leads but is basically useless in court.  Similarly, hearsay (basically, what someone said to another person about past events) is generally inadmissible and will be of limited value.

Think about the ending of your case before you even begin.  When I was a prosecutor, before I indicted any case, I thought through the trial and the sentencing phases of the case.  And in doing so, I thought about how I would attack my case if I were on the other side.  This helps avoid the cognitive problem we now call confirmation bias. Again, from Holmes, this time from the Black Peter:

“One should always look for a possible alternative, and provide against it.  It is the first rule of criminal investigation.”

I’ll go through additional lessons and tips in future articles, such as a look at Sherlock Holmes’ interviewing techniques. You can see me discuss these and other points, such as a look at how Sherlock Holmes’ mind worked, in a webinar that I did for the Federal Bar Association in January.  I’ll be giving a new version of this presentation for another FBA chapter in California on June 4 – please join if you’re interested!

I was a federal prosecutor for 11 years and also worked at big law firms for 10 years. I now am a solo practitioner focusing on white-collar criminal defense, health care fraud, and data analytics in litigation.