What Police Knew

Most important of the commodities traded by the police was information—the content, of course, but equally the flow. Tsar Nicholas's secret police were his best—and surprisingly accurate and useful—source of information on the state of his realm in all respects.¹⁴⁹ Their hierarchical organization, military-style command and communications, and strategically located outposts made the police efficient conveyors.

The content of what the police knew or could discover was even more important.

The state had tackled occult crime from the start. Ordeals—God's testimony—were intended to solve crimes that might not have wit­nesses (individual heresy, infanticide) or where witnesses were party to the offense (simony, adultery, incest, sodomy, concubinage, brib­ery) or could not testify (bestiality).¹⁵⁵ Torture, too, was meant to uncover hidden evidence. But over time, the judiciary's verdicts came to depend not on supernatural and forced testimony but on circumstantial evidence and other simply empirical and scientific data. As oaths, ordeals, and torture were replaced by observational, scrutinized evidence, policing as an epistemological tool came into its own.

The judiciary found and punished ever more offenders as it grew better able to marshal evidence, constructing convincing cases. And as more merciful sanctions set in, ending popular resistance to how offenders were penalized, only faulty evidence impeded the state in prosecuting criminals. The civil law's inquisitorial system was more targeted than the common law, with its adversarial confrontation before a jury. Prosecutors' discretion whether to pursue cases varied, from largely none in nations such as Finland, Italy, and Germany to a great deal in the Netherlands and Norway.¹⁵⁶ But after preliminary investigation, all civil law prosecutors brought forth those cases they considered winnable, thus increasing their hit rate.

The jury in turn evolved into a mechanism for evaluating evi­dence. Having been a group of self-informing peers, picked largely because they already knew the circumstances, the jury turned into a forum for weighing evidence of thirdhand events. In the Middle Ages, they had been selected for their personal knowledge of the case. But such contact eventually disqualified jurors as nonimpartial.¹⁵8

Once the oath, with its appeal to supernatural intervention, no longer promised certainty and a verdict, jurors had to evaluate the evidence.¹⁵⁹ Sealed in the black box of the jury room, they judged witnesses' credibility, their testimony's verifiability. “Beyond a rea­sonable doubt” evolved as the evidentiary legal standard at about the same time as the seventeenth century's scientific revolution made testimony of the senses and empiricism more generally the most trusted form of knowledge.¹⁶⁰

The state won cases largely on the evidence supplied from citizens and rounded up by police legwork. Before technology helped them much, the police turned to an unsavory ecosystem of spies, snitches, snoops, stooges, and informers who passed on gossip, denuncia­tions, and hints, all prompted by an array of mixed motives: pay, reward, exemption from punishment, and sometimes even public- spiritedness. Napoleon's concierges or the dvorniks of St. Petersburg were only the most regularized of the bunch.¹⁶¹ Plato required citi­zens to report impieties they came across.¹⁶² In early modern Eng­land, those who turned in criminals had their own crimes pardoned. Informers ratted on tariff and customs violators and religious dis­senters in the seventeenth century and then on violators of Sabba­tarian laws and public cursers in the eighteenth.

Old-regime France required brothel madams to file reports on their clients. Prostitutes were handy sources of information in the nineteenth century. French detectives believed that mouchards (informants) were as useful to tracking down crime as smoke was to locating fire. Chinese Communists took a similar approach in the late 1940s.¹⁶⁵ The tsarist police enlisted house porters and night watchmen.¹⁶⁶ The Soviet and Nazi secret police relied heavily on denunciations, and no system has ever roped in proportionately as many snitches as the East German Stasi. Former criminals in China today provide the bulk of informants and information.¹⁶⁷ In mod­ern liberal democracies, too, informers pull their weight, encourag­ing religious extremists to become terrorists, for example, and thus leading to their arrest.¹⁶⁸ The recent lavish development of con­spiracy law has incentivized criminals to rat on their fellow offend- ers.¹⁶9 But, like entrapment, relying on informers means that the police must encourage crime in order then to solve it.

Bounties made lay citizens collaborators with the police. In ideol­ogized states, whether religious or political, denunciation enforced orthodoxy.¹⁷⁰ But denouncers have been found everywhere. In ancient Greece, sycophants were those who turned in offenders for a share of the spoils. In the Middle Ages, denunciation allowed pros­ecution even of those whom no one wished to officially accuse.¹⁷¹ In seventeenth-century England, neighbors denounced each other at extraordinary rates for sexual deviance.¹⁷² In fourteenth-century Venice, carved lions' mouths on the sides of buildings hid letter slots for denunciations.

Informers played crucial roles in early modern Europe. Eight per­cent of Florence's police budget went to paying them, and another 12 percent to reward those who reported violations of peace and treaty agreements. Minor public officials, the sindaci, were selected for each neighborhood, tasked with reporting crime and rewarded by the case.¹⁷⁵ In seventeenth-century England, rewards for evidence lead­ing to conviction became a lucrative element of the justice system— apprehending a highway robber paid £40 and the offender's horse, arms, and money. Informants on illegal London gin shops collected half the fine, as did their colleagues in the American colonies who reported shoddy merchandise or retail fraud.¹⁷⁶ More than 90 per­cent of prosecutions under the Statute of Apprentices (1563) were brought by private informers. Many made a profession of informing. In 1699, the “Tyburn Ticket” was granted to those who helped con­vict burglars, shoplifters, and horse thieves, exempting them from duties in local offices—such as policing their neighborhood as con­stables. In 1720, the total reward for the conviction of a robber in London was £140, thrice a journeyman's annual income.¹⁷⁷

Such incentives continue today. Besides the rewards posted on the most-wanted list, information leading to conviction pays off as immunity from prosecution for those who testify as state's evidence. Bounty hunters are rewarded, as are whistle-blowers—in tax fraud, proportionately to the recouped sums.¹⁷⁸ US state attorney gener­als' offices keep the fines they impose on banks for malfeasance.¹⁷⁹ Law enforcement agencies retain some of the proceeds of confiscated crime-related property.¹⁸⁰ Prosecution of some crimes relies heavily on covert information, for example, insider trading, where bounties can reach 10 percent of penalties (which can be thrice the illicit prof­its).

Other surreptitious means of information gathering have evolved with the technology at hand. For centuries, private letters have been opened by state officials, leading to an arms race of competing techniques of sealing, opening, and resealing them. Eavesdropping in the literal sense has occurred ever since there were eaves to stand under, the edge of the eaves marking the legal limit of the private, domestic space.¹⁸² Electronic devices now make for more convenient listening, wiretapping phones, secretly recording conversations, and audio-surveilling homes and offices. Today, we debate government access to email and social media.

Much more of a revolution and not just amplifying the circuits of witnessing was the growing acceptance of empirical and scientific evidence independent of human testimony. The judicial system's evidentiary base gradually shifted from confession and witnessing to evidence that existed autonomously of anyone involved in the offense. Insisting on eyewitness testimony and confession, Roman law had discounted circumstantial evidence. Interrogation, with tor­ture as its most extreme form, never got beyond witnesses, including possible perpetrators, and their limited and self-interested vantage. Today we forbid torture, not only for humanitarian motives but also for epistemological reasons as likely to produce self-serving and unreliable information. And we understand eyewitness testimony to be inherently unreliable, colored by all manner of influence and but a dim reflection of what happened.¹⁸³ The testimony of facts and the traces of our biological and physical trails instead supply the most illuminating evidence. We are spared the forceful extraction of con­fession from our souls by the betrayal of our bodies. Indicia, once spurned as merely epiphenomenal, have returned as the queen of evidence.

The new evidentiary gold standard relied on induction from knowledge of the world to conclude guilt or innocence, entirely independent of whether the acts in question had been witnessed or even perceived. Knowledge could be uncovered regardless of humans encountering it, having it, or testifying to it. One of Roman law's two queen proofs, eyewitness, came to be understood as unre­liable and often outright misleading. Indeed, false or mistaken eyewitness accounts have proven to be the preeminent cause of wrongful convictions.¹⁸⁴ The apparently stolid facts presented by the world instead took their place. Forensic investigations have been performed at least since the physician Antistius claimed that only one of Julius Caesar's twenty-three stab wounds had been fatal and even two centuries earlier in China. Sung Tz'u's thirteenth­century Chinese text on forensic investigation, The Washing Away of Wrongs, explained how to distinguish between corpses killed before or after being burned or inundated, how to discern the difference between hanging and strangulation or between drowning and being drowned, and how to distinguish murders from suicides com­mitted so as falsely to implicate others. With a deft noirish touch, he recommended checking the anuses of unexpectedly deceased elderly husbands married to young wives—to look for hidden pene­tration wounds.¹⁸⁵ In early modern Europe, mothers who gave birth while alone and whose child died were often suspected of infan­ticide. Had the infant been stillborn or killed postpartum? In the absence of an unimplicated eyewitness, the lungs of the infant were submerged in water. If they floated, that was considered proof that the child, born alive, had taken its first gasps to inflate them.¹⁸⁶

Early modern Russian peasants killed by beating on planks placed on their victims' swaddled stomachs. This technique destroyed the victims' innards without leaving external traces but was rendered obsolete once coroners began their forensic investigations in the late nineteenth century.¹⁸⁷ In 1905, two murderers were hanged on the basis of a thumbprint on a cash box.¹⁸⁸ In the late nineteenth century, crime photography began to reveal evidence obscure to the naked eye. The disturbed dew drops on a park bench next to the body of an apparent suicide, for example, betrayed the presence of someone else at the scene.¹⁸⁹ In such cases—whatever the merits of the science of the day—nature spoke directly, though not unaided, to the court. We now take cross-examining nature on the stand— the dramatis personae of countless courtroom dramas—so much for granted that we are blind to the significance of the change.

Fingerprinting emblematized the justice system's embrace of the new scientific evidence. “Every contact leaves a trace” was the man­tra of the investigatory work that underlay forensic science.¹⁹⁰ Fin­gerprinting was used sporadically in the ancient world and likely developed first in China. It caught on systematically in British India and then in Europe and the Americas in the 1890s. The first trial where fingerprinting provided the main evidence was held in India in 1898. The court accepted that the partial print left behind proved the suspect had touched a box with stolen money and so convicted him of burglary. But it was still unwilling to accept by the implied logic that he had also killed the box's owner.¹⁹¹

Subsequent technologies have sharpened our observational lens, often demonstrating that earlier techniques were faulty or unreli­able. Crime scenes were photographed to scale, footprints measured and cast in plaster, soles typologized, as were automobile and bicy­cle tires later.¹⁹² Particulate residue in earwax as well as nail and hair clippings gave evidence of activities undertaken even months ear­lier. Starting in the 1930s, blood typing began to crudely associate suspects with offenses. DNA testing has since become an exact and reliable science.¹⁹³ Together with genetic databases, it now allows criminals to be identified even decades after their offense. Dental records began identifying murder victims. Tooth isotope analysis revealed where victims had grown up and sometimes events of their lives—whether they had been weaned and if they had ever starved. Toxicology pinpointed more wrongful poison deaths. Microscopic examination allowed crime's implements to be identified. Ballistics, the forensic analysis of bullets and firearms, became its own dis­cipline in the late eighteenth century.¹⁹⁴ Chemistry was turned to detecting forgeries—of checks, wills, or artworks.

Over time, some technologies were displaced or discredited. Now supplanted by DNA analysis, the once popular microscopic inspection of hair proved largely worthless.¹⁹⁵ Graphology held the nineteenth-century world in thrall. It still retains adherents but has been largely discredited—indeed, handwriting itself is a technology in steep decline. Alphonse Bertillon—inventor of the mugshot— helped convict Alfred Dreyfus, the Jewish officer accused of treason against France in 1894, with convoluted claims that Dreyfus him­self had written incriminating documents using a tracing method as though someone were forging his actual hand, thus giving him deniability.¹⁹6 Not that we have freed ourselves of charlatanry. Doubtful technologies of alleged expertise still sway juries, such as blood-spatter analysis, forensic investigation of clothing, and body­language scrutiny.¹⁹⁷ DNA analysis has instead become the gold standard, revisiting and upending past wrongful convictions based on more primitive technologies. “DNA testing is to justice what the telescope is for the stars,” one of its early practitioners put it, “a way to see things as they really are. It is a revelation machine.”¹⁹⁸ But its precision can and has been overstated, and its seeming accuracy has created problems. A German swab-manufacturing technician (dubbed the “Phantom of Heilbronn”) inadvertently spread his own DNA to evidentiary samples and so appeared to be a prolific serial offender. Transplant recipients receive and incorporate the DNA of their donors and can leave it behind as traces. And people may plant misleading DNA at crime scenes.¹⁹⁹ More generally, such evidence supplies evermore ammunition for the common law's adversarial system. Experts duel for both sides, leaving juries to sort out whose testimony deserves credence.²⁰⁰

Keeping track of previous offenders has been vital. Mutilation and branding were once both an element of punishment and a conve­nient indicator of recidivism. Now we use the everyday singularities of the human body.²⁰¹ The British compiled a Register of Distinct Marks in the 1870s on the assumption that criminals' bodies were individual enough to allow identification.²⁰² Bertillon systematized this approach in the 1880s by measuring bodily dimensions for indi­vidual identification. This cumbersome anthropometrical method, Bertillonage, was overtaken by the (re)discovery late in the cen­tury that fingerprints were unique.²⁰³ Fingerprinting also had the enormous advantage of combining a system of identification—like Bertillonage—with the evaluation of traces left behind at the crime scene. And today fingerprints can even be dated.²⁰⁴ The more fin­gerprints, the more useful the database, and so the race was on to expand the files. By 1906, Australian police were routinely collecting fingerprints of known “bad characters under arrest.” By the 1950s, the volume had become so large that some jurisdictions discontinued

printing minors.²⁰⁵ In the United States, the FBI amassed some eighty million fingerprints, only some of which belonged to crimi­nals. Reformers pushed for universal or at least broad fingerprinting of all citizens.²⁰⁶

From the 1840s, photography, too, was used to identify offend­ers. The Prevention of Crimes Act of 1871 in England established a national photographic record.²⁰⁷ In the 1880s, the mugshot was standardized by Bertillon. Unable to send photographs other than by mail, he also developed a system of written portraits to telegraph descriptions of suspects. This foreshadowed the algorithms that contemporary face-recognition technology uses to express images in machine-searchable formats. But, given the technology of the day, in fact most of these late nineteenth-century written portraits were largely identical, and few suspects without identifying marks were arrested on this basis.²⁰⁸ Like fingerprints, DNA records even of nonconvicts are kept today. In France as of 2003, DNA profiles were collected from suspected offenders, with fines and jail for refusals, and of all inmates serving longer sentences.²⁰⁹