Macro, Micro, Meso: Core Transitions in Forensic Science*

Exploration of a topic I've spoken on before (2023 and 2024, and at AAFS 2025) and a chapter I wrote. Oh, and read to the end.

It’s All About Perspective

Forensic science* has seen several watershed shifts in perspective that have led to its current operational state. They run from the macro to the micro to the meso, seemingly out of order with their scale nomenclature (“big,” “middle,” “tiny”).

Dammit, Jim, I’m a Doctor!

The first was in 529, when Emperor Justinian approved the Codex Constitutionum, an extensive reconfiguration of old and new Roman law. In it, doctors were acknowledged as witnesses who could provide judgments based on their expertise and not only on eyewitness testimony; today, this privilege is called being an expert witness.¹ Doctors having the ability to testify using their expertise led to that profession’s involvement with legal proceedings that included trauma, death, and disease—the purview of medical science. It’s little wonder, then, that forensic science* began with medicine and then forensic medicine. Up through the 17th and 18th centuries, “forensics” was body-centered and the domain of medical doctors only. Little else mattered besides the body; the remaining investigation involved police shoe leather and knocking on doors, as far as the doctors were concerned. A clear delineation between “police” and “experts” was also created from this shift in perspective. Murder was the morally important crime and the only one deemed significant enough for “important people” to be involved. Thus, forensic science* had a macro-perspective: The body was the scene.

Iocane powder, anyone?

The second shift came with the advent of toxicology, which shifted the perspective to things that could not be seen with the layperson’s eye, requiring interpretation to the layperson, who had to infer the truth. This is a micro-perspective, seeking out molecules and interpretations not only beyond the layperson but beyond what the medical doctors knew (much to their chagrin). The foundation for this had been laid with allowing doctors to speak about things only they knew and could interpret, but toxicology took it a step further (or smaller) by advancing their expertise on poisons. Poisoning was very popular during the 17th and 18th centuries for a number of reasons. There were lots of rats, so arsenic was a common household good to poison them. Diseases were common, so a person dying from a “sickness” wasn’t particularly shocking or worthy of the authorities’ notice. Poisons and their metabolism were largely unstudied (until Orfila), so back to a lack of detection. The development of toxicology to address the rash of poisonings meant that the abstraction to the chemical level moved “forensic” work away from the body and into the laboratory: The body went to the morgue (doctors) but the evidence went to the chemistry bench (toxicology). The toxicologist’s expertise broached the barrier that medicine had claimed for so long (Horrors!). The doctor’s description could be countered by tissue analysis revealing things that could not be seen but could be proven, nevertheless. The science* still needed to be comprehended by the judge and jury, so the legal requirements continued to control science: It was not and is not peer-to-peer communication. But that’s a topic for another post.

Setting the scene

The third and final shift was in 1883, when Hans Gross published arguably the first forensic textbook, Handbuch für Untersuchungsrichter als System der Kriminalistik (Handbook for Examining Magistrates as a System of Criminalistics). Gross’ early experience on the job with a wide variety of cases, from murders to arson to fraud, led him to realize that his formal education had not prepared him for the scope of crime and the breadth of expertise needed to investigate them properly. Gross pored over the natural, medical, physical, and social sciences, to re-educate himself. Gross wrote his manual in clear language that anyone with a basic education could understand. He also coined the word kriminalistik (criminalistics) to describe the sciences* as applied to criminal investigations, as opposed to criminology, the study of criminal behavior in society. This set forensic science* further apart from policing. His book was immensely popular: When he died in 1915, the book had been published in seven editions and had been translated into a number of foreign languages.

Gross recognized that it was the crime scene and not the body that was of paramount importance in a criminal investigation. His book designated the crime scene “as a distinct analytical space, bounded conceptually and operationally by explicit rules of practice, and recognized as such by forensic investigators and the broader public alike.”² Prior to Gross, unless the body held some obvious connection to the perpetrator, the investigator had no methods to connect the suspect to the scene or the victim.

This involved the use of proxy data, like trace evidence and fingerprints, that allowed for the comparison of evidence that was left behind to a set of records without the person needing to be present. As Gross noted:

“The trace of a crime discovered and turned to good account, a correct sketch be it ever so simple, a microscopic slide, a deciphered correspondence, a photograph of a person or object, a tattooing, a restored piece of burnt paper, a careful survey, a thousand more material things are all examples of incorruptible, disinterested, and enduring testimony from which mistaken, inaccurate, and biased perceptions, as well as evil intention, perjury, and unlawful co-operation, are excluded…

Although Faulds and Henry considered the potential of fingerprinting in criminal investigations, it was Edmund Locard who realized Gross' dream of making the crime scene and its contents the focus of forensic activities. With his access to the criminal files that contained fingerprints of arrestees, Locard could now identify individuals who had been at a crime scene without them having to be present. Additionally, this allowed for the recognition of a fingerprint left at a scene or on an object to be the goal of a search in the files (the database) with no person of interest identified.³

Let’s Do the Time Warp Again

As a historical (reconstructive) science,⁴ forensic science* has the ability to jump between times and spaces, giving it the scope of activities from the macro (doctors and the deceased body) to meso (the scene) to micro (trace evidence and fingerprints) across its development. This perspective emphasizes identifying which sciences are historical rather than debating whether history is a science and grants forensic scientists* three key abilities:⁵

1. Selectivity: The capacity to determine what evidence is relevant in an investigation. Given that a crime scene can contain numerous items, this ability is crucial for focusing on what truly matters.

2. Simultaneity: The ability to analyze events across different times and locations concurrently. This allows for the comparison of multiple crime scenes or the examination of a series of crimes. This is achieved by maintaining an objective distance from the events, which facilitates understanding and comparison.

3. Scale-shifting: The ease with which forensic scientists* can transition between macroscopic, mesocopic, and microscopic perspectives. This enables the tracing of connections, such as linking fibers to clothing, then to manufacturing facilities, and finally to specific production batches.

These abilities collectively assist forensic scientists* in uncovering the relationships between individuals, locations, and objects involved in criminal activities. More importantly, this provides the basis for possible source and activity interpretations.

A subsequent Substack will tease out more about selectivity, forensic chemistry, and German industry in the 19th century (wut?).

NB: The chapter I mentioned in the subtitle was, “Epistemology of Forensic Science,” in Research Handbook on Forensic Science & Criminal Justice, edited by Carole McCartney and Aaron Amankwaa, Edward Elgar Publishing, 2025.

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1. Houck, M.M., Funk, C., Feder, H. and Feder, H.A., 2018. Successful expert testimony, 5th edition. CRC Press.

2. Burney, I., 2013. Our environment in miniature: dust and the early twentieth-century forensic imagination. Representations, 121(1), pp.31-59.

3. Locard, E., 1909. L'identification des récidivistes. Maloine.

4. A point I elaborated on in my 2010 PhD dissertation but is not new with me. Ralph Turner, who created the forensic science* program at Michigan State University in 1947, had this in his lecture notes: “Criminal Investigation—Reconstruction of a prior event, Archaeology to auto accident.” Ralph Turner Collection Research, Course Materials CJ815—Criminal Investigation (1965-1979), Folder 42, Box 1674, Collection UA17.149. Michigan State University Special Collections. (Thanks, Toby!)

5. JL Gaddis, The Landscape of History (Oxford University Press, 2002).