Forensic Fact vs. Fiction

On this episode of Inside the FBI, we separate myth from reality about how the Bureau uses science to process crime scenes. For a full transcript and additional resources, visit

Jennifer-Leigh Oprihory: On a recent episode of our podcast, we gave you a passport to the world of the FBI’s Evidence Response Teams.

These frontline responders deploy to crime scenes to document them and collect evidence—and then ensure that evidence gets to the FBI Laboratory quickly and safely. These experts also commonly take the stand in court to reconstruct crime scenes for juries who can’t visit crime scenes firsthand, as well as defend the integrity of the evidence they find and the manner in which it’s collected.

But for many jurors, it’s TV depictions of crime scene investigations that shape their understandings of what kinds of evidence people can actually gather, what kinds of scientific analysis are possible, and how long these kinds of processes take. So an unofficial—but significant—part of the job is to separate fact from fiction and debunk what’s been dubbed the “CSI Effect.”

On this episode of our podcast, we’ll explain the CSI Effect—and then let Evidence Response Team members and forensics experts set the record straight about what your favorite crime show likely got wrong. We’ll also walk through what it’s really like when ERTs use science to process crime scenes.

I’m Jennifer-Leigh Oprihory, and this is Inside the FBI.

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Oprihory: No matter where you get your headlines—whether it’s local newspapers, national TV, or your favorite podcast—you’ve likely come across the term the CSI Effect.

The phenomenon broadly refers to the way that television depictions of crime scene investigations shape people’s views of what kinds of evidence can be collected from a crime scene and how long it takes to do so.

This effect can be seemingly benign—after all, a forensic science student isn’t going to use their favorite TV show to study for a final exam, and medical examiners aren’t tested against what they’ve seen on the small screen.

But when someone is summoned to jury duty, that’s when the CSI Effect can be problematic.

Heather Thew: I think that because you've got this nice, neat, tidy package where they wanna highlight some of the really fancy techniques that are available, they use them all. They get multiple, different forms of evidence that may not be what is real at a real scene.

The CSI Effects [sic] tends to make juries say, "Well, why didn't you get DNA off of everything there? Or latent fingerprints everywhere." And the reality is that those things aren't everywhere. The absence of evidence sometimes is okay, too. You know, it tells us another story.

Oprihory: That was Supervisory Special Agent Heather Thew, an instructor with the FBI’s Virginia-based Evidence Response Team Unit, or ERTU, which trains Evidence Response Team members to approach crime scenes the FBI way and to be able to explain that process in court.

According to Tom Duffy—a retired agent who has led training for the unit—ERT members who are called to testify during court cases make it a priority to set the record straight and teach non-experts what actually happens at a crime scene. This is because, as Duffy explains:

Tom Duffy: When the juries are meeting you, they're equating you to what they see on TV.

Oprihory: For this reason, when Duffy took the stand, he preferred to explain both what investigative steps he carried out at a given scene and how he actually performed them.

Duffy: The juries love it. I'm educating them. There's an old line, "educated consumer is your best customer."

Oprihory: This emphasis on detail doesn’t only ensure that jurors are informed about process.

Duffy said it also helps win their confidence by demonstrating that the Evidence Response Team didn’t overlook any steps when processing the crime scene.

Similarly, he notes, ERTs devote a good chunk of their time to photographing all aspects of crime scenes, making sure they present a complete visual story of what these locations looked like before and after they undertook their work.

According to Duffy, the time and effort ERTs spend processing crime scenes, as well as the number of people and gear available to get the job done, make a strong impression on juries.

Duffy: I think those are two biggest things. And when we get onto the stand, I tell my folks, "Educate them. Tell the prosecutor that you want to show them, because it adds to your credibility; it shows 'em it's not TV, and they say, 'Wow, they over-document so much. There's no way they made a mistake.' It instantly adds so much credibility, and you win the jury. You win the jury, you win the case."

Oprihory: This isn’t all to say that crime shows are inherently bad. On the contrary, they can help people envision a future for themselves in law enforcement. Special Agent Brandon Strait, who works in the FBI’s Washington Field Office and serves on its Evidence Response Team, said these fictional programs helped influence his decision to join the Bureau.

Brandon Strait: I was in a prior health care career, and I was intrigued by people that I was treating who were in law enforcement and how cool their jobs just seemed compared to mine. But then it was probably the TV shows, like all the "CSI," all the things that glamorize and romanticize the job that I was probably watching, and it, like, had an impact somehow.

Oprihory: But the stark contrast between what crime scene investigation looks like in real life versus on the small screen is also a big reason why Supervisory Special Agent Gene Lanzillo—lead instructor for the FBI’s Crime Scene Administration and Management Basic course—cautions that an interest in the TV version of crime scene investigation doesn’t automatically make you well-suited for ERT.

Gene Lanzillo: All those series are great shows, but the reality is, they don't show you 16 hours on scene in Tyvek with blood. They don't show you that, which I understand. We want somebody, though, that will say, "I'm happy to be here with these people that work hard and do great things."

Oprihory: Now that we’ve established what isn’t in the realm of reality for Evidence Response Teams, let’s take a look at what is.

Oprihory: Evidence Response Teams pull members from across the FBI, in terms of both geography and job descriptions, since anyone employed by the Bureau—whether they’re an agent, analyst, or professional staff member—can throw their hat in the ring.

Some of these people had past lives as scientists—whether they worked in the field or in the lab. In some cases, these backgrounds had direct ties to forensic science. Take Supervisory Special Agent Thew, for example.

Thew: So, I was an archaeologist, anthropologist and, by education, and I've worked in the field of archeology, forensic anthropology, and DNA analysis. So, kind of a varied scientific background with kind of a heavy emphasis in forensic science.

So, ERT was really why I joined the Bureau. So, I became a special agent knowing that there was such a thing as the Evidence Response Team, definitely wanting to be a part of that team and being able to work crime scenes and complex scenes worldwide.

Oprihory: For others, working on an ERT was a different kind of pivot.

Supervisory Special Agent Martha Hufford, another member of the ERTU, was working as an undergraduate biochemistry researcher when the criminal justice bug bit her.

Martha Hufford: I loved that work, and I wanted to keep doing it, but while I was working at that lab, I started volunteering for a domestic violence shelter, and I was trained as a rape victim advocate and a domestic violence victim advocate. And I saw some things that just completely changed my perspective.

Oprihory: When it came time to choose between applying for another research gig or a job in a Kansas City crime lab working with DNA, she said it was a no-brainer.

Hufford: And I've been doing that ever since. That was 21 years ago that I went into law enforcement.

Oprihory: She went on to work counterterrorism and surveillance and serve on the FBI El Paso Field Office’s Evidence Response Team before eventually joining the Evidence Response Team Unit she now calls home.

Hufford: You know, I just, I keep coming back to forensics. I can't get—can’t get away from it.

Oprihory: But while preexisting forensic expertise can be helpful when joining an Evidence Response Team, it’s more of the exception than the rule.

For this reason, the ERTU gives all personnel who take ERT Basic—the entry-level program that equips an individual to respond to crime scenes as an official ERT member—an in-depth course in the scientific tools and techniques needed to make sense of a crime scene.

Let’s dive into some of them.

If we were to play a game of word association, and I said “forensic science,” there’s a solid chance your response would be “fingerprints.” But how do investigators actually find and capture them?

In addition to looking for evidence of human touch with the naked eye, investigators can use something called an alternate light source—which emits a single, set wavelength of light. This light can illuminate things that would otherwise be invisible, such as substances found in fingerprints, bodily fluids, and even the bleach that criminals can use to try and cover their tracks.

Once someone spots these prints, step two is to figure out how to develop them, or make them visible to the naked eye.

Evidence Response Teams have a few options for doing this.

One is dusting—or applying a specialized powder to an area until it begins to cling to substances in the fingerprint, which, in turn, makes it readily visible. Investigators can then use an adhesive surface—like Scotch tape—to lift these prints from where they were found and place them onto a fingerprint card for FBI Lab processing.

Another method involves heating up a far more common chemical—super glue—in a controlled area until it becomes a vapor that adheres to the fingerprints in a similar way to the powder, making them show up on a surface.

After this process—formally known as cyanoacrylate fuming—is completed, ERT members can also dust the developed prints to lift them, or even create a cast of them, to send to the Lab.

ERT investigators can also use dyes—such as amido black and leucocrystal violet—to help make prints more readily visible so that they can be photographed for processing by the FBI Lab.

The option—or options—ERTs end up using chiefly depends on the surface the print is found on. And since some print-developing options can’t be used after another one has been performed, it’s as much of an art as a science, whose process is ultimately at the discretion of an ERT team lead.

Evidence Response Teams can also capture impression evidence, such as tire tracks, shoe prints, or toolmarks, to gain insights into what went down at a crime scene.

While ERTs can take casts of obvious impressions in mud or even snow, they can also use a device known as an electrostatic dust lifter to capture evidence of footprints or other impressions left behind in dirt or similarly dusty substances.

This device works by creating an electrostatic reaction between the impression and a sheet of mylar—yes, the balloon material. The end result is a literal picture of the impression that can then be sent to the FBI Laboratory.

Now, let’s talk blood.

The first rule of finding blood at a crime scene is: not calling it blood without proof.

This is where presumptive blood testing comes in.

Hufford: So, we all have a pretty good idea of what we know blood looks like, but I'm sure we've also seen things at times that looks an awful lot like blood but isn't blood.

You know, sometimes, really dried up soda stains can look a little bit like blood. Paint. There's a variety of things that can look similar to blood. And, so, what we do, if we're not certain if we want to collect an item, is we do a simple test just to look for the heme—

Oprihory: That’s just a technical term for iron.

Hufford: —in blood. We call it presumptive because it's not a confirmatory test for blood.

Oprihory: While the FBI Laboratory is equipped to determine whether a sample is actual blood, ERTs can’t do that at a scene. Instead, they use one of two tools to get the presumptive result.

Option one is the chemical phenolpthalein. When a potential blood stain is first treated with phenolpthalein and then hydrogen peroxide, the stain will turn a reddish color when it's likely blood.

Option two is a product called Hemastix. These strips of chemically-treated paper have tips that change color when they come into contact with the iron in blood.

No matter which test an ERT picks, the results help them determine whether or not they should collect a sample to send to the FBI Laboratory.

But potential blood stains aren’t always readily apparent when investigators arrive at a crime scene. This is where the next two tools of the ERT trade—the chemical luminol and the alternate light source—come into play.

Luminol allows investigators to illuminate invisible blood stains by causing them to glow. This works because when luminol, followed by hydrogen peroxide, is applied to a potential blood stain, the iron present in blood causes a chemical reaction that produces a blue glow visible when investigators shine an alternate light source on it. These illuminated stains can also be photographed as evidence.

Similarly, the teams can use other dye processes to help make stains easier to see and photograph.

But as vital as it can be to capture images and/or samples of presumptive bloodstains, Evidence Response Teams can’t forget another piece of the investigative puzzle: DNA.

In addition to the analytical methods we’ve already explained, ERT members are also trained to scope crime scenes for potential sources of DNA evidence. They use their knowledge of the case and professional discretion to determine what items they’ll test for genetic material.

These considerations can be complicated, Hufford says, since sources of DNA evidence vary between scenes. Even if an ERT member discovers a presumptive blood stain that looks convincingly real, they can’t automatically assume they know where the blood came from.

Hufford: It’s asking yourself the question of, "Okay, is there any chance that any of this blood is someone other than my victim? How many of these stains do I want to collect, to order, to rule out that possibility?"

Sometimes, we just don't know, and we have to hedge our bets and make the best decision we can. I've worked scenes where there's blood in literally every room, for whatever reason—someone cut themselves, there was an argument, someone hurt each other—and the blood may or may not be related to what happened. So that... it could be blood, it could be invisible. It could be an item that we hoped was handled multiple times, enough times that we might be able to get enough DNA to get a profile from. We really don't know.

That's what makes this job challenging is that we really don't know a lot what we're going to get or what we hope to get. We just have to kind of keep thinking it through and making the best decisions we can.

Oprihory: Sometimes, ERTs will decide to package an entire item for transport to the FBI Laboratory for testing. But in cases where that’s not logistically possible, Hufford explains, teams can either cut out a sample of the item or take a swab of it.

Hufford: This is not black and white. There's a lot of thought that has to go into it. And you have to really understand the circumstances of the crime. You have to understand the circumstances of where we're searching, why we're searching, who was in there, what exactly we're looking for.

Are we looking for people who, anybody who may have lived in the house? So we're looking for anybody who may have been in the house? Or are we only looking for people who could have participated in that crime?

There's so many variables to consider that what we're really trying to create are little mini computers that can go in there and ask themselves these questions. You know, what is my best chance for getting probative DNA samples at this scene?

Oprihory: The tools and techniques we’ve discussed here are just a sampling of what Evidence Response Team members can leverage to help the FBI Laboratory make sense of what went down at a crime scene.

Once they’ve graduated from the ERT Basic Course—the foundational training for all full-fledged ERT members—they can always broaden their forensic skillsets by taking additional coursework offered by the Evidence Response Team Unit.

Likewise, Duffy explained, the FBI’s Evidence Response Team Unit has a research and development section dedicated to making sure ERTs can leverage the most cutting-edge advancements possible when processing crime scenes.

Duffy: Their goal is to stay current with technology, do research, better cameras, better alternate light sources. We have 3D scanners that I can put a scanner in the middle of that room there and walk out and five minutes later, come back in, it'll render everything, you know, digitally, which is fantastic.

Oprihory: And since the ERTU is part of the FBI Laboratory, he says, it’s always on the lookout for opportunities to borrow lessons learned.

Duffy: When they learn new techniques, they share 'em with us, vice versa. If we go out to, like, a Las Vegas bombing, and let's say a team member comes up with a new way of doing things, like, you know what? That's fantastic. Let's borrow that.

We work hand in hand with the Lab, our R&D folks, to make sure that when they learn something, we come up with something, our biggest role is to incorporate it into our curriculum, and you know, we vet it, approve it. We rewrite the curriculum, put it out there. And then, we put it out to the teams, as well.

Oprihory: At the end of the day, a breakthrough for one is a breakthrough for all. This is because the more effectively ERTs can uncover and collect evidence from crime scenes, the more efficiently the FBI can solve cases, bring criminals to justice, and give closure to victims and their families.

Thanks for joining us today as we worked to separate forensic rumor—and the CSI Effect—from the real work our ERTs do every day.

This has been another production of Inside the FBI. You can follow us on your favorite podcast player, including Spotify, Apple Podcasts, or Google Podcasts. You can also subscribe to email alerts about new episodes at

I’m Jennifer-Leigh Oprihory from the FBI’s Office of Public Affairs. Thanks again for tuning in.