By Deepti Govind
From around the end of the 19th century until the middle of the 20th century, a French forensic scientist developed several key scientific methods of analysis that are still in use and remain one part of the bedrock of forensic science. Dr. Edmond Locard was born in Saint-Chamond on Nov. 13, 1877. His first job was assisting a criminologist and professor. Through the early days of his career, Locard partnered with anthropologist Alphonse Bertillon, who was known for his system of identifying criminals based on their body measurements, and even worked as a medical examiner.
In 1910, the Lyon Police Department is said to have granted Locard the opportunity to create the first crime investigation laboratory where he could analyze evidence from crime scenes in a previously unused attic space. Over a research career that continued until his death in 1966, Locard pioneered what has become a critical aspect of the criminal investigation and justice process. Even today, the Federal Bureau of Investigation (FBI) acknowledges and credits Locard’s biggest contribution to forensic science while talking about its Evidence Response Teams (or ERTs): Locard’s Exchange Principle.
What exactly does this principle say and how was it used in Locard’s days, when were ERTs established in the United States, and how do these critical FBI teams work? We answer those questions in this piece.
Locard’s Exchange Principle
Locard is said to have written many publications during his lifetime, including a seven-volume series called Traité de Criminalistique or Treaty of Criminalistics. He’s the one who said various scientific processes — chemistry, biology, physics, metallurgy, etc. — should be applied to crime scenes, Supervisory Special Agent Gene Lanzillo, a veteran FBI ERT member and instructor with the Evidence Response Team Unit (ERTU) said in an episode of the Bureau’s Inside the FBI podcast series.
As we mentioned earlier, though, Locard’s biggest contribution to the world of forensic science was a theory that came to be known as Locard’s Exchange Principle. The basic idea sounds simple enough to us today: every single contact leaves a trace. It is on the basis of that principle that even today across the country law enforcement agencies, whether it’s the FBI or a three-person police department out in the middle of Iowa, are all doing the same thing: looking for that contact.
What exactly did Locard write, or say, about this principle? Although over time it has come to be understood with the shortened phrase “with contact between two items, there will be an exchange,” that’s not what Locard wrote down. What he did write was: “It is impossible for a criminal to act, especially considering the intensity of a crime, without leaving traces of this presence.” In other words, Locard believed that no matter where criminals go or what they do, they are bound to leave something at the scene of the crime. At the same time, they also end up taking something away with them.
A post on HowStuffWorks goes on to describe a true crime example of how Locard tested his principle out during one of his investigations from the year 1912, which also gives an interesting example of how forensic science and evidence collection helps. Here’s an edited version of the example on HowStuffWorks:
A Frenchwoman named Marie Latelle was found dead in her parents’ home. The police had questioned her boyfriend at the time, Emile Gourbin, but he claimed he had been playing cards with some friends the night of the murder. And after the friends were questioned, Gourbin’s alibi appeared to check out. But when Locard looked at the corpse, he was led to believe otherwise. An examination of Latelle’s body led to clear evidence that she was strangled to death. Locard had also scraped underneath Gourbin’s fingernails for skin cell samples.
He later viewed the results of those samples underneath a microscope and noticed a bit of pink dust among the samples, which he established was make-up of some sort. Although makeup was popular in 1912, it was by no means mass-produced, and this was reason enough for Locard to dig a little deeper. He eventually found a chemist who developed a custom powder for Latelle, and a match was made. Gourbin confessed to the murder and to the fact that he had tricked his friends into going along with his alibi by setting the clock in the game room ahead.
The FBI’s Evidence Response Teams
There were ad hoc ERTs in the 1980s in the United States. The Bureau also has a history of making instructional videos to teach local law enforcement how to process crime scenes. But the first official ERTs were created before one major event, according to Special Agent Lanzillo — the Oklahoma City Bombing. What the Bureau teaches now in the ERT Basic Course is an amalgamation of art, science, and legal policies and requirements that’s both rooted in this past but also looks to the future.
ERTs are, effectively, a link between the crime scene and the investigating laboratory. They’re the “eyes and ears” of a case, according to Supervisory Special Agent Heather Thew per the FBI podcast. The FBI Laboratory — with facilities in Huntsville, Alabama, and Quantico, Virginia — employs some of the world’s foremost forensic science experts, the Bureau says. But it’s logically impossible to send them to every single crime scene the Bureau investigates. And that’s where ERTs come in. In a nutshell, the job of the ERTs is to collect evidence and get it to the Lab in the best condition possible. Of course, the practical application comes with its own set of challenges and nuances.
As the eyes and ears of a case, the ERTs are a case agent’s search team and have to identify evidence at the scene using various tools and techniques — such as alternate light sources, fingerprint techniques, looking for latent fingerprints, etc. Then the ERTs have to collect and preserve these things in the best condition possible. They also ensure crime scenes are closed off to potential outside contamination, document them in photos and drawings, and scour every inch for potential evidence.
Another responsibility of the ERTs is to search for potential proof of foul play, including evidence they can see — like footprints in the snow or a gun that a perpetrator might’ve accidentally left behind — and other types of evidence that their specialized training teaches them how to illuminate, develop, or extract — such as blood spatter that suspects mistakenly think they’ve cleaned up enough to hide, latent fingerprints, and/or DNA.
In the foundational training for ERT members, known as the ERT Crime Scene Administration and Management Basic Course, they are taught to use a 12-step process when approaching crime scenes. The first and the last steps bookend the investigative process and are: getting ready for the crime scene investigation and releasing the crime scene. The FBI podcast only partially lists the remaining 10 steps as taking entry, evidence, and exit photographs; creating a sketch of the scene; searching the scene; and recording and collecting evidence.
There’s flexibility with the 10 steps that happen in between. Sometimes, they may even occur simultaneously. For example, if we consider a house as the location of the crime, one ERT member could be sketching a diagram on the first floor of the house, while another bags evidence upstairs. The process is designed such that teams can process crime scenes in a methodical, detail-oriented way without needing excessive amounts of equipment, gear, and — most importantly — manpower.
Every one of the FBI’s 56 field offices has its own ERT. The size of each team typically ranges from eight to 40 people, with the overall ERT community being around 2,100 FBI personnel strong, per the Bureau. Each field office’s special agent in charge controls its ERT and decides whether and how the team will deploy — either piecemeal or as a collective — in most cases. ERTs typically help out in various kinds of cases, ranging from recovery of human remains to body searches, to agent-involved shootings.
“Any time you have a source that requires a high level of sophistication and specificity, they may ask for the Evidence Response Team,” Special Agent Lanzillo says on the podcast. Under certain circumstances, the ERTU will also be in charge of deployments. This can happen during major events, and examples include the Las Vegas shooting, the Boston Marathon bombing, 9/11, or the Pulse Nightclub shooting. “We will, here as a Headquarters element, contact other divisions and say, ‘We need to deploy you in support of this,'” Lanzillo adds.
The goal of these teams, as Supervisory Special Agent Tom Duffy puts it, is to “take the jury and put them in there, looking over our shoulders virtually, as we encounter things and find things and document, so they’re confident that we processed it the correct way. They are confident that we found everything.” The efforts of ERTs on the ground can help ensure justice is served in the courtroom.
Within ERTs, there are also various sub-divisions like the Underwater Evidence Program, the Forensic Canine Program, and the Hazardous Evidence Response Team Program. We will explore these, and what it takes to be part of the Bureau’s ERTs in a separate piece in the future.