Measuring Deception: A Review of Tremors in the Blood

In Tremors in the Blood: Murder, Obsession and the Birth of the Lie Detector, Amit Katwala tells the story of an invention that promised to make deception physically visible. By recording changes in breathing, pulse, and blood pressure, the polygraph appeared to offer police and courts something they had always wanted: an objective method for separating truth from lies.

Yet the device never truly measured lies. It measured physiological arousal and depended on an examiner to decide what those bodily changes meant. Nervousness could resemble guilt, while confidence and self-control could disguise deception. Despite this fundamental problem, the polygraph spread through American policing, employment screening, intelligence work, popular culture, and private life.

Katwala approaches this history through a combination of true crime, biography, psychology, and technological cautionary tale. At the center are three striking figures: progressive police chief August Vollmer, intellectually driven inventor John Larson, and charismatic showman Leonarde Keeler. Their collaboration helped create the modern polygraph, but disagreements over its purpose and reliability eventually pulled them apart.

The result is an atmospheric and often fascinating account of how an experimental instrument acquired an authority far greater than its scientific foundations justified.

A Murder and a Machine

The book’s narrative hook is the murder of Anna Wilkens in 1922. Her husband, Henry Wilkens, arrived at a San Francisco hospital covered in her blood and claimed that bandits had attacked the couple. Suspicion soon shifted toward him. Was he an innocent husband traumatized by his wife’s murder, or had he helped arrange the crime?

The case presented investigators with a familiar problem. Physical evidence could suggest possibilities, and witnesses could offer competing stories, but none of it necessarily revealed what had happened inside a suspect’s mind. A machine that could expose concealed knowledge or detect a dishonest answer seemed capable of cutting through uncertainty.

Katwala uses the Wilkens investigation to introduce the early lie detector as both a scientific experiment and an instrument of police power. Its presence changes the emotional dynamics of an interrogation even before any chart is interpreted. The wires, cuffs, tubes, needles, and moving lines make the suspect’s body appear to be testifying independently of the person’s words.

This is one of the book’s most important insights. The polygraph’s influence has never depended entirely on its accuracy. Its theatrical power matters just as much. A suspect who believes that the machine cannot be deceived may confess, alter a story, or reveal information. The instrument can therefore produce results without reliably detecting lies.

That distinction—between detecting deception and persuading people that deception has been detected—runs throughout the book.

Three Men and Three Visions

The history of the polygraph becomes compelling largely because of the personalities involved in its development.

August Vollmer was a reform-minded police chief who wanted to modernize law enforcement. At a time when policing was frequently associated with corruption, brutality, and poorly trained officers, Vollmer promoted education, professional standards, scientific methods, and cooperation with academic researchers. His goal was not merely to solve more crimes but to replace coercive practices with supposedly rational ones.

John Larson represented the scientific conscience of the project. Trained in both policing and academic research, he hoped physiological measurement might improve investigations while reducing reliance on intimidation and physical violence. He was ambitious and deeply committed to the idea that criminal justice could benefit from psychology and medicine.

But Larson was also cautious. He understood that bodily responses were not identical to lies and that test results required interpretation. The more popular and powerful the device became, the more troubled he grew about exaggerations of its capabilities.

Leonarde Keeler embodied a very different approach. Fascinated by magic, performance, technology, and crime detection, he recognized the polygraph’s dramatic potential. He made the instrument more portable and helped transform it into a recognizable symbol of scientific policing. Where Larson saw an experimental research tool surrounded by qualifications, Keeler saw a practical device that could be demonstrated, marketed, taught, and deployed.

Katwala does not reduce the conflict to a simple opposition between an honest scientist and a dishonest promoter. Keeler believed in the technology and helped make it usable. Larson’s own ambitions and emotional volatility also complicated his relationship with the invention. Still, their disagreement reflects a recurring tension in technological history: the person most careful about a tool’s limitations may lose control of it to the person best able to sell its promise.

The Desire for Mechanical Truth

The appeal of the lie detector is easy to understand. Human beings are poor at determining whether others are lying. Confidence can be mistaken for honesty, nervousness for guilt, and social prejudice for intuition. Investigators are susceptible to confirmation bias and may interpret every reaction as evidence supporting an existing theory.

A machine seems to offer escape from those weaknesses. Numbers, charts, and mechanical traces look neutral. They suggest that truth exists as a measurable signal, independent of personality, status, and human judgment.

Katwala shows that this appearance of objectivity can be dangerously misleading. The machine measures physical responses, but an examiner chooses the questions, establishes the procedure, compares reactions, and interprets the resulting lines. Human judgment is not removed; it is concealed behind technical equipment.

That concealment can make subjective conclusions more persuasive. A detective saying “I think you are lying” invites skepticism. A detective saying “the machine proves you are lying” invokes the authority of science, even when the underlying inference remains uncertain.

The polygraph’s cultural success therefore reveals something broader than the history of a single invention. People want truth to be mechanically accessible. They want ambiguity converted into a chart and doubt replaced by a verdict. The stronger that desire becomes, the easier it is to overlook the distance between what a technology measures and what its users claim it measures.

Science, Pseudoscience, and Interrogation

Katwala is strongest when explaining that the polygraph occupies an unstable space between scientific instrument and interrogation prop.

The device can accurately record physiological changes. The controversy lies in interpreting those changes. A racing pulse or altered breathing pattern may indicate fear, stress, embarrassment, anger, confusion, trauma, or awareness of being judged. None of those reactions necessarily establishes deception.

The setting itself creates anxiety. An innocent person accused of murder may be more frightened than a practiced liar. A guilty subject may remain calm, manipulate breathing, or simply believe the falsehood being told. Questions can also carry different emotional meanings for different people.

This does not mean a polygraph session can never reveal useful information. A skilled examiner may identify contradictions, provoke admissions, or discover investigative leads. But usefulness in an interrogation is not the same as scientific proof of lying.

Katwala carefully explores this ambiguity. The machine may appear successful because suspects sometimes confess after being tested. Yet a confession can result from psychological pressure, belief in the machine, or fear that the examiner already knows the truth. Such outcomes demonstrate the power of the procedure, not necessarily the accuracy of the instrument.

This difference matters because false confidence can cause investigators to abandon other possibilities. Once a chart is treated as proof, an innocent person’s denials may appear to be further evidence of dishonesty. Meanwhile, a deceptive person who “passes” can be removed from suspicion prematurely.

From Reform to Control

One of the history’s central ironies is that the lie detector emerged partly from a humane reform movement. Vollmer and Larson hoped scientific methods might replace violent interrogation and arbitrary judgment. In that respect, the machine represented progress.

But a technology created to limit abuse can produce new forms of coercion. The polygraph did not need to beat a suspect physically to exert pressure. Its authority could make resistance appear futile. The subject was invited to believe that the body would betray any attempt at concealment.

This psychological pressure became more troubling as the device moved beyond criminal investigations. Polygraphs were used to screen employees, test loyalty, investigate private behavior, and assess people who had not been accused of any specific offense. In such settings, refusal to submit could itself be interpreted as suspicious.

Katwala’s history illustrates how technologies often expand beyond their original purpose. A tool introduced for exceptional cases becomes routine. A procedure justified as voluntary becomes difficult to refuse. A device promoted as an aid to human judgment begins replacing that judgment.

The most consequential question is therefore not simply whether the machine works. It is who controls it, who must submit to it, how its results are used, and whether the person being tested has any meaningful way to challenge the conclusion.

The Tragedy of John Larson

Larson provides the book with much of its emotional depth. He was instrumental in developing the technology but became increasingly disturbed by its misuse and commercial promotion. The invention that might have secured his legacy instead became a source of frustration and regret.

His predicament is painfully familiar. Inventors cannot determine how institutions will use what they create. Once a device attracts money, publicity, and government interest, caution becomes an obstacle. Nuance is difficult to market, while certainty sells easily.

Larson’s reservations did not erase his responsibility for the machine, but they make him a more complicated figure than either visionary or victim. He wanted science to improve justice, yet his work helped lend scientific legitimacy to questionable conclusions. He recognized the problem, but recognition could not reverse the polygraph’s expansion.

Katwala presents this trajectory as both personal tragedy and historical warning. The development of technology is not complete when a device begins functioning. Its public meaning, commercial uses, and institutional consequences may prove more important than the intentions of its creator.

Larson’s eventual disillusionment gives Tremors in the Blood a melancholic quality. The story is not about a successful invention later revealed as imperfect. It is about a disputed technology whose limitations were visible early, even as its reputation continued to grow.

Leonarde Keeler and the Performance of Authority

If Larson embodies caution, Keeler represents confidence and spectacle. He understood that technology gains power through presentation. The machinery, technical language, controlled setting, and examiner’s manner could create an experience that felt authoritative.

Keeler’s background and showmanship make him one of the book’s most entertaining characters. His association with magic is especially appropriate because the polygraph itself depends partly on managing belief. Like a stage illusion, its effect is shaped by what the audience thinks it is witnessing.

That comparison does not mean every examiner is deliberately deceiving a subject. Many practitioners sincerely believe in the method. But sincerity does not eliminate performance. The examiner still establishes an atmosphere in which the instrument appears to possess almost supernatural access to hidden truth.

Keeler’s success also demonstrates why simplified claims often overpower careful ones. “This machine records physiological reactions that may correlate with deception under certain conditions” is scientifically responsible but institutionally weak. “This machine can tell whether you are lying” is memorable, frightening, and easy to sell.

The triumph of the second claim over the first is at the heart of the book.

True Crime as a Vehicle for Intellectual History

Katwala avoids turning the book into a dry technical history by organizing it around murders, investigations, trials, rivalries, and damaged relationships. The true-crime episodes give immediate stakes to debates about accuracy. A mistaken interpretation is not merely a laboratory error; it can redirect an investigation, influence a jury, or destroy a life.

This narrative method works particularly well because lie detection sits at the intersection of science and storytelling. Investigators build narratives from evidence, suspects offer alternative accounts, and examiners claim to identify which story the body confirms. Every case becomes a contest over who controls the meaning of the physical traces.

At times, however, the large cast and movement among cases can make the narrative feel crowded. Readers primarily interested in the scientific validity of the polygraph may find the biographical detail excessive, while readers expecting a straightforward murder mystery may be surprised by the extended history of policing and psychology.

The subtitle accurately signals the book’s range: murder, obsession, and invention receive nearly equal attention. It is not simply a history of a machine, nor is it only an account of one criminal case. It is a study of how personalities, institutions, cultural desires, and technological claims combined to create a modern myth.

A Warning for the Age of Artificial Intelligence

Although much of the book concerns the early twentieth century, its implications are unmistakably contemporary. New systems now claim to infer emotions, intentions, credibility, or suspicious behavior from facial movements, voice patterns, gaze, language, and other data.

The polygraph’s history offers a framework for evaluating those claims. A system may measure something accurately without measuring what its promoters say it measures. It may detect changes in voice without detecting dishonesty, identify facial movements without identifying emotion, or recognize statistical patterns without understanding intention.

The same institutional pressures also remain. Governments and employers want efficient methods for screening large numbers of people. Companies benefit from presenting uncertain systems as objective. Users may trust a technical score more than a human judgment, even when the score reflects hidden assumptions and unreliable correlations.

Katwala’s warning is not that all technology is fraudulent. It is that technical complexity can disguise conceptual weakness. The crucial questions are simple: What is actually being measured? How strong is the connection between that measurement and the conclusion? Who interprets the result? What happens when the system is wrong?

The history of the lie detector demonstrates that weak scientific foundations do not necessarily prevent widespread adoption. In some cases, the appearance of certainty is more valuable to institutions than certainty itself.

Strengths

The book’s principal strengths include:

• A compelling central idea: The invention of the polygraph becomes a broader story about society’s desire to mechanize truth.
• Memorable historical figures: Vollmer, Larson, and Keeler embody distinct approaches to policing, science, and commercial promotion.
• An effective combination of genres: Katwala blends true crime, biography, psychology, and technological history without losing sight of the human consequences.
• Moral and contemporary relevance: The book connects naturally to present-day systems that claim to infer hidden mental states from bodily or behavioral data.
• A nuanced argument: The polygraph is presented neither as a miraculous detector nor as a meaningless box, but as a flawed measurement device whose psychological and institutional power exceeds its reliability.

Katwala is particularly effective at showing how respectable motives can lead to harmful outcomes. The original hope of reducing police brutality was not absurd or malicious. The tragedy lies in the transformation of a limited investigative aid into an allegedly objective judge of human honesty.

Limitations

The book’s most significant weakness is that its narrative can become diffuse. The shifting cases, scientific debates, personal relationships, and institutional developments do not always fit together with equal smoothness. Some sections read like a thriller, while others resemble a group biography or a history of criminal psychology.

The murder cases are often engrossing, but the emphasis on suspense can occasionally compete with the scientific discussion. Readers seeking a systematic evaluation of modern polygraph research may want more sustained analysis of methodology, error rates, countermeasures, and the differences among testing procedures.

The principal inventors also dominate the story. This is understandable, but more attention to the experiences of test subjects could have strengthened the book’s examination of power. The machine’s history is not only about the people who constructed and promoted it; it is also about those pressured to accept its judgments.

Finally, the book’s recurring warning about technological overconfidence is persuasive but sometimes repetitive. Once the central distinction between physiological arousal and deception is established, later examples reinforce rather than substantially complicate the argument.

Final Assessment

Tremors in the Blood is a lively, intelligent history of the polygraph and the people who tried to turn the hidden act of deception into a visible bodily signal. Amit Katwala uses murder investigations and personal rivalries to examine a much larger question: why are human beings so eager to surrender uncertainty to machines?

The book’s answer is both psychological and institutional. We distrust our own ability to judge honesty, but we also crave definitive conclusions. Police departments, courts, employers, and security agencies benefit from tools that convert suspicion into apparent evidence. The polygraph satisfies that desire through machinery, charts, technical language, and performance—even when the interpretation remains deeply uncertain.

John Larson’s disillusionment supplies the story’s tragic center, while Leonarde Keeler’s promotional genius explains how the invention escaped the control of its more cautious creators. Their conflict is not merely a historical curiosity. It anticipates current disputes over algorithms and artificial intelligence systems whose impressive outputs may conceal uncertain assumptions.

The book occasionally feels crowded, and readers looking for either a pure true-crime thriller or a comprehensive scientific critique may find its hybrid structure uneven. Nevertheless, that mixture is also its greatest distinction. Katwala demonstrates that the lie detector cannot be understood solely as a machine. It is a cultural object built from scientific aspiration, police authority, commercial ambition, theatrical persuasion, and the persistent fantasy that truth leaves an unmistakable physical trace.

Rating: 3.5 out of 5 stars

Tremors in the Blood is especially well suited to readers interested in true crime, the history of policing, forensic psychology, pseudoscience, technological ethics, and miscarriages of justice. Its enduring lesson is simple but important: a machine’s ability to produce measurements should never be confused with its ability to reveal the truth.