Tremors in the Blood

Tremors in the Blood is a work of narrative nonfiction that traces the invention and spread of the polygraph, commonly known as the lie detector, through two murder cases separated by 15 years. Based on historical sources, the book argues that the men who created the lie detector hoped to make justice fairer but instead unleashed a tool they could not control, one that reflected their own flaws and amplified existing prejudices.

The first case opens on May 30, 1922, when Henry Wilkens, a 36-year-old German-born mechanic, drove his family home to San Francisco from a camping trip. A dark blue Hudson touring car pursued the family through thick fog and forced their car to the curb. A masked gunman demanded money; Henry handed over $300, but when the man reached for his wife Anna's rings, Henry reached for his own gun. The bandit fired first, and Anna died on the operating table.

The investigation stalled quickly. Henry misidentified the pursuing vehicle, contradicting a witness who insisted it was a Hudson. Two days later, police brought in Walter and Arthur Castor, brothers with criminal records, after they paid for a car repair with a hundred-dollar bill. Henry failed to identify either man in a lineup, but as the suspects filed out, he caught Arthur's eye and winked, a detail the detectives missed. Newspapers soon revealed that Anna had filed for divorce weeks earlier, accusing Henry of cruelty and infidelity. The Castors' alibis collapsed, and police discovered that Henry and Walter had once worked together, a fact Henry denied. With both brothers in flight and Henry refusing to change his story, the police turned to a new machine being developed across the bay in Berkeley.

The narrative then shifts to the origins of the polygraph. August Vollmer, Berkeley's visionary police chief, had spent years modernizing law enforcement: He established officer training programs, recruited college-educated policemen, and rejected the "third degree," the widespread practice of beating suspects to extract confessions. In February 1921, after reading a paper by Harvard psychologist William Moulton Marston on blood pressure and deception, Vollmer asked John Larson, a rookie officer and the only PhD on any American police force, to build a lie-detecting device. Larson, a 28-year-old born in Nova Scotia, combined blood pressure monitoring with breathing-rate measurement and built a prototype he called the "cardio-pneumo-psychograph," which became known as the polygraph. In its first criminal case, Larson extracted a confession from a dormitory theft suspect but later doubted whether the subject's responses reflected guilt about the crime or personal distress, beginning a pattern of doubt that deepened throughout his career.

Seventeen-year-old Leonarde Keeler, the charismatic son of a Berkeley poet, became Larson's assistant and began improving the device, making it portable and replacing fragile smoked-paper records with ink on white paper. Their different temperaments planted the seeds of a lifelong rivalry: Larson was patient and methodical, while Keeler was headstrong and commercially minded.

On June 9, 1922, Larson tested Henry at the Hall of Justice. Henry was agitated, and the test had to be stopped three times. Once he calmed, his responses showed no dramatic spikes, and Larson told the press that Henry appeared truthful. When Larson examined the chart later, however, he considered it "doubtful." That evening, a DA investigator followed Henry to a secret meeting with the Castors' brother, where Henry boasted about passing the test.

The DA's office cracked the case with a simpler trick: Investigators planted a sobbing teenager in a cell next to the recaptured Arthur Castor. Tormented by the boy's cries and haunted by nightmares, Arthur confessed. He described how Henry had signaled the brothers at the campground, paid them, and arranged for Walter to follow the family's car and stage the robbery. Weeks later, police cornered Walter at his family's home. In less than three minutes, he killed Detective Tim Bailly and his lover, Annie Downs, and then shot himself. Larson read about the bloodshed with horror, recognizing that the lie detector's failure to expose Henry may have contributed to the deaths.

Henry's affair with Helen Lange, Anna's younger sister, which began while Anna was hospitalized weeks before the murder, provided the prosecution's motive. Lange testified that she found Anna's supposedly stolen rings hidden in a bureau drawer. Henry's first trial ended in a hung jury; his retrial ended in acquittal after jurors misunderstood the judge's instructions as a directive to find Henry not guilty. Several jurors later expressed regret. Henry died in 1953 without confessing. In 1923, the case Frye v. United States established a legal standard that effectively barred polygraph evidence from most courtrooms for the next century by requiring that new scientific technology gain "general acceptance" in its field before being admitted as evidence.

The book's second case unfolds in Depression-era Chicago. On October 8, 1935, Max Dent, a federal narcotics informant, was shot four times in the back near his family's home. Police focused on Joseph Rappaport, a 30-year-old drug dealer whom Dent had helped convict. Rappaport's alibi collapsed, and a note in Dent's handwriting named Rappaport as a threat to his life.

By this time, the three creators of the lie detector had all converged on Chicago, and the relationship between Larson and Keeler had deteriorated into open hostility. Larson accused Keeler of commercializing the polygraph recklessly by selling tests to businesses and putting the machine in unqualified hands. Keeler countered that Larson was consumed by jealousy. Vollmer, exhausted from years of mediating, stopped answering Larson's letters.

Rappaport was convicted and sentenced to death, but over the next 13 months, he received five stays of execution as his attorneys uncovered witnesses contradicting key testimony. On March 1, 1937, the day of the scheduled execution, Rappaport's sister Rose accosted Governor Henry Horner at a train station, pleading for her brother's life. Horner, who had faith in Keeler's polygraph, suggested Rappaport submit to a test. That evening, Keeler set up his machine in Rappaport's death cell as officials watched through the bars. The test violated every protocol Keeler himself had established: The room was crowded, the lights flickered as guards tested the electric chair next door, and the examination lasted less than an hour. Keeler concluded that Rappaport had lied and telephoned Horner. At five minutes past midnight, Rappaport was executed in the electric chair.

The epilogue traces the aftermath. Keeler, haunted by the case and by venomous letters from Rose Rappaport, descended into alcoholism and died of a stroke in 1949 at age 45. His wife, Kay Keeler, a pioneering forensic handwriting expert, had been killed in a 1944 plane crash while serving with the Women's Auxiliary Service Pilots. Vollmer, diagnosed with Parkinson's disease after his wife's death, shot himself in his garden in 1955. Larson spent his remaining years fighting the machine's spread, describing it before his death in 1965 as "a Frankenstein's monster, which I have spent over forty years in combatting." Marston, whose research inspired the device, pivoted to entertainment and created the comic book character Wonder Woman in 1941; the character's signature weapon, the "lasso of truth," echoed his deception research.

The book closes by examining new lie detection technologies, from brain fingerprinting, an EEG-based test that claims to detect recognition of familiar information, to AI-powered facial analysis and eye-tracking systems. Each repeats the polygraph's pattern of premature adoption. Millions of tests are still conducted annually despite the scientific consensus that no single physiological indicator of deception holds true for everyone. The book demonstrates that the appeal of a "truth machine" persists, and so do its dangers.