Blood, Powder, and Residue

How Crime Labs Translate Evidence into Proof

Beth A. Bechky

• Publisher: Princeton University Press
• Year: 2021
• ISBN:
  9780691205854
• Topic: Social Sciences
• Subtopic: Criminology
• Index: Social Sciences

A rare behind-the-scenes look at the work of forensic scientists The findings of forensic science—from DNA profiles and chemical identifications of illegal drugs to comparisons of bullets, fingerprints, and shoeprints—are widely used in police investigations and courtroom proceedings. While we recognize the significance of this evidence for criminal justice, the actual work of forensic scientists is rarely examined and largely misunderstood. Blood, Powder, and Residue goes inside a metropolitan crime laboratory to shed light on the complex social forces that underlie the analysis of forensic evidence.Drawing on eighteen months of rigorous fieldwork in a crime lab of a major metro area, Beth Bechky tells the stories of the forensic scientists who struggle to deliver unbiased science while under intense pressure from adversarial lawyers, escalating standards of evidence, and critical public scrutiny. Bechky brings to life the daily challenges these scientists face, from the painstaking screening and testing of evidence to making communal decisions about writing up the lab report, all while worrying about attorneys asking them uninformed questions in court. She shows how the work of forensic scientists is fraught with the tensions of serving justice—constantly having to anticipate the expectations of the world of law and the assumptions of the public—while also staying true to their scientific ideals. Blood, Powder, and Residue offers a vivid and sometimes harrowing picture of the lives of highly trained experts tasked with translating their knowledge for others who depend on it to deliver justice.

Part 1

THE WORK OF CRIMINALISTS

Chapter 1

FORENSIC SCIENTISTS AT THE LAB BENCH

Taming, Questioning, and Framing the Evidence

Forensic scientists are applied scientists who work in the service of the criminal justice system. In many ways, the work that forensic scientists perform in Metropolitan County Crime Laboratory (MCCL) resembles the work performed by laboratory technicians across the spectrum of science.¹ The analytic practices they use, in terms of biology or chemistry, are similar to those one would see in academic, industrial, or hospital labs. Yet the purposes toward which forensic scientists put these techniques are different. Unlike other scientists, their goal is to analyze possible material links between a suspect and a crime.

Forensic scientists work on analyzing evidence for use in the criminal justice system. As the term “forensic science” indicates, criminalists employ the methodical and systematic approaches of science and apply them to evidentiary materials used in the law. Their work therefore requires not only scientific acumen, but also an understanding of the standards and requirements of the legal system. Like all science, it depends on routines: scientists meticulously follow procedure to avoid contamination and produce consistent results. While rote practice does structure their work, they also rely on the aesthetics of their materials, using embodied aspects of their craft—that is, their five senses, along with their expert knowledge—to help them make judgments.

Forensic science work follows the same overarching path across all disciplines at MCCL. In each unit they analyze evidence from crime scenes by taming, questioning, and framing the evidence. The evidence arrives in the basement of MCCL wrapped in neat paper and plastic packages, belying the messiness of their contents. The items inside, often soiled from the crime scene, now need to be tamed, to be made more standard and orderly for scientific investigation. Forensic scientists carefully lay out the items on their benches, readying them while considering what analyses to do.

For example, in the process of screening evidence from a rape scene, a DNA analyst puts on gloves to remove a pair of underwear from a paper bag, scrutinizing them closely to see where she might find biological materials. She photographs them, cuts off small pieces to try to extract DNA, and draws a diagram in her notes indicating where the samples were taken. Firearms examiners and fingerprint analysts treat their evidence gingerly as well, first examining items thoroughly and carefully, so as not to accidentally fire a loaded gun or damage any potential prints. Care with materials is a hallmark of all scientific work and carries through every step of analyzing evidence at MCCL.²

In their approach to analyzing evidence, criminalists hold a neutral stance toward the interpretation of their results. Criminalists identify as scientists: they believe strongly in the tenets and practices of the scientific method, and, when expressing their views on their work, they speak in terms of the norms of science.³ They remark on their own objectivity and neutrality as they pursue the results of their cases, making remarks such as “I don’t have a horse in the race.”

And, like science more generally, forensic science is organized communally. Criminalists rely on two scientific communities for guidance: the broader forensic science community and their local laboratory colleagues. Within the laboratory, criminalists review one another’s work and rely upon their colleagues for training, support, troubleshooting, and decision-making. Additionally, laboratories communicate with one another about the appropriate protocols and practices to use, in online forums, by phone, and in person during audits by the forensic science laboratory association and at professional meetings and conferences.

After questioning the evidence to determine what it shows, criminalists narrow their findings in order to draw conclusions, which they share in written reports and courtroom testimony. These reports of conclusions require framing, in which criminalists represent their results and work processes in ways that will be legible to a broader audience: lawyers, judges, juries, and the media. To do so, analysts in the lab collectively craft reports and the statements within them, to present a compelling image of their expertise that is consistent across cases. They are scientists whose primary audience, in many ways, is the people outside of the science community.

This chapter will introduce you to the work of the criminalists at MCCL. Analysts tame the evidence that comes into the lab from messy crime scenes, question it with specific techniques to discern what the evidence demonstrates, and then frame the evidence in a report that is both a scientific and legal document. While all the work at MCCL reflects similar broad scientific conventions, the distinctions between the units’ work are striking as well. I describe in detail the practices of each unit, which differ in their techniques, materials, types of output, and style of interpretation. This chapter investigates the different paths that evidence takes through these different disciplines, and the ways each kind of forensic scientist performs their work.

WHO ARE CRIMINALISTS?

Before describing the practices of the disciplines and units of the crime lab, we first need to know more about where criminalists come from.

Forensic scientists arrive at the crime laboratory with similar backgrounds: typically a bachelors’ degree in biology or chemistry. After passing a battery of tests and undergoing a panel interview, they are hired into a specific unit, such as forensic biology or toxicology. The practices of forensic science vary by discipline, and criminalists use distinct techniques to examine different forms of evidence: in narcotics, wet chemistry is used to identify drugs, while firearms examiners use comparative microscopy to compare bullets. Consequently, once assigned to a unit, criminalists undergo extensive specialized training. Training is particularly intense in forensic biology (whose most common output is DNA profiling), where analysts train in-house for nine months before being certified to work on cases. And in firearms, examiners attend a statewide training program for a year, and then train in the lab for an additional year before even starting casework.

Because the complexity of the techniques, practices, and cases varies across disciplines, the time and effort criminalists need to create and report conclusions about the evidence also varies. Major cases, which include serious felonies like homicide or rape, are complex, involving extensive evidence collection requiring analysis of multiple items. Consequently, the DNA analysts and firearms examiners I observed who worked on these major cases were proud if they completed sixty to a hundred in a year. In contrast, toxicologists, in half a day, could analyze forty-five blood samples simultaneously for DUI (driving under the influence) cases, and narcotics analysts could assess many types of drug samples in only ten to fifteen minutes each. These specialized fields, then, while grouped collectively under “forensic science,” actually exhibit striking differences, both in the science involved and in the daily work of their practitioners.

It wasn’t always this way. Forensic science was once the province of generalists. Senior criminalists I met often spoke about their early years in the field, where “I did everything: blood typing, firearms examination, narcotics.” This generational difference helps explain why, despite changes to the field, senior managers still expect all forensic scientists to have a similar skill base and regard them as potentially interchangeable across units. When the lab director at MCCL planned to swap two criminalists between the narcotics and firearms units, he reminded everyone at the monthly staff meeting, “You are all criminalists, and you should be able to work in any unit in the lab.”

Despite such sentiments, over the last twenty years, as changes in science and technology have refined forms of analysis, criminalists have become specialists. Some do switch units, primarily as a result of their own interests and wishes. Among criminalists at MCCL, the most common career move is from toxicology into narcotics, since these units share analytical techniques. Only occasionally do toxicologists or narcotics analysts move into a unit that analyzes major cases, such as firearms examination or DNA profiling.

The differences across units—in techniques, work, and relationships within the broader system of criminal justice—result in distinct social practices within each unit.

Forensic biology is the largest unit in the lab with eighteen members, two-thirds of whom are women. The unit’s nickname, “DNA princesses,” refers not only to gender but to the status of DNA profiling. As the most recently scientifically and legally legitimated technique of forensic science, DNA profiling is held up as the gold standard of forensic evidence. Other groups envy the resources the unit commands in terms of equipment, funding, grants, and staff.

Comparative evidence, on the other hand, which contains the firearms examination lab, is the smallest: seven members, predominantly men. Also working on major cases, this unit practices the most traditional forensic science, using techniques developed inside law enforcement. The chemistry unit, which contains narcotics and trace analysis, and the toxicology unit handle much larger caseloads of simpler drug identification and intoxication cases. Even though the two units perform similar chemical identification techniques, they have discrete work practices. In toxicology, the nine analysts have less autonomy. The work is more rote and requires the least amount of training. The work of the eight narcotics analysts, on the other hand, is more independent and varied.

Thus, while the criminalists at MCCL share scientific assumptions and practices, these differences in casework, training and techniques lead to different work practices within each unit.

WORK PRACTICES OF FORENSIC BIOLOGY: LEGITIMATED SCIENTIFIC INQUIRY USING STATISTICAL INFERENCE

Ellie is leaning over a paper-covered square table in the DNA lab’s screening room. She lays out a white dress, the evidence from a sexual assault case, underneath four large hanging ceiling lights. Two months earlier, Ellie had tested the swabs from the rape kit: the intimate swabs taken from a victim’s body at the hospital. Ellie says, “Those were negative [for DNA], so as a last resort I have this grab bag of clothing.”

Failing to find the perpetrator’s DNA in the rape kit—the most likely place, given the details of the police report—Ellie extends her search to the victim’s clothes. The victim, attacked in an alley, told the police that she did not think the man wore a condom. So, after the rape kit came back negative, Ellie next ran the underwear, because “the underwear would have draining because the victim wore it afterward.” Again, no DNA.

Now she is testing the dress, she says, because “you start with what you think is the most probative.” That is, Ellie started with what is most likely to result in evidence that would directly link to the suspected crime, and later moved to less likely evidence: the dress. This is because, Ellie explains, “on the dress, the suspect can say all sorts of things … if it is on the outside of the dress, that is easier to explain away. He can say, ‘I did my thing on her’ and then just get public exposure, a much lesser crime.”

The dress has some reddish-brown stains on the front and back, as well as some hairs. Ellie removes the hairs with tweezers, puts them in an envelope, and adds to her running notes on the case their location on the dress. Climbing up a stepladder with a camera, she snaps several pictures of the front of the dress, and then flips it over to take several more pictures, again noting the locations of the stains. Then she turns the dress inside out and photographs it that way as well. Between each set of photos she replaces her gloves so that DNA is not transferred to the camera for the next analyst using it.

Because this is a large piece of evidence, Ellie first tries to pinpoint the location of any biological fluids by using an ALS, or alternative light source. Semen fluoresces (glows) at 460 to 470 wavelengths, so the light source is focused at that wavelength. Ellie and I both put on orange goggles; then she turns off the overhead lights and flips on the blue ALS. After checking the quality control item (a piece of cardboard with semen on it) to make sure it turns bright yellow, she focuses the light on the front of the dress. She sees several bright yellow spots and circles them with a black Sharpie. “Because I didn’t find anything on the underwear, this is surprising,” she says. “It may still be nothing.”

Since other fluids aside from semen fluoresce at the same wavelength, Ellie, after scanning the entire dress with the light, moves on to a specific test for semen: an acid phosphatase (AP) test. We go out to the serology reagent refrigerator in the main lab, which holds shared chemicals for common biological fluid tests, to get the necessary chemical reagents (substances that cause or detect chemical reactions) for the AP test. Since there are so many locations on the dress to test, Ellie needs to make an unusually large amount.

Ellie mixes the reagents in the proportions required in the protocol and puts them in a large tube. Allison, sitting nearby at her bench, jokes about the amount of reagent: “What are you AP’ing, an elephant?” We laugh, and Ellie borrows a timer from her. She pulls a quality control strip out of the freezer, and we return to the screening room. The strip turns purple in the proper number of seconds after she drops the AP onto it. This means the test she has prepared can correctly identify semen.

And yet, when Ellie performs the same test on the circled locations on the dress, no purple appears. The dress, ultimately, had no semen on it that Ellie could find.

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Ellie’s screening activities are typical of the first step of casework in the forensic biology unit, whose primary focus is DNA profiling. All DNA analysts in the MCCL unit perform all the tasks in this process: screening the evidence, running the profile on the biological sample, interpreting the results from the instrument, and writing the report.⁴

The vibe of the DNA unit is that of any busy biology lab. Analysts in white coats sit or stand at their benches, peering through microscopes, wiping down workspaces with alcohol, pipetting samples...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Contents
• Preface
• Introduction: Welcome to the Crime Lab
• Part 1: The Work of Criminalists
• Part 2: The Culture of Criminalists
• Part 3: The Struggles of Criminalists
• Conclusion
• Appendix: Case Notes on an Ethnography of a Crime Laboratory
• Acknowledgments
• Notes
• References
• Index