After the Civil War ended, Pinkerton returned to Chicago to resume direction of his agency. Superintendents George Bangs and Francis Warner had managed the day-to-day enterprise of the business during the war years; in that time, they had overseen the opening of a second and third Pinkerton office in, respectively. New York City and Philadelphia. The Confederacy snuffed, Allan Pinkerton could now again concentrate on an assortment of swindlers, cheats, confidence men and other no-gooders plaguing the big cities and little towns of America.

William came with him, joined now by second son, Robert. The two assisted their father by researching the habits and experiences of not only specific criminals on the lam, but of the criminal mind, in general. William loved the chase – he was happiest when in the saddle riding down some outlaw across Boston or across the Midwest wheat fields; location didn't matter, he enjoyed being detective. And he did it well. Robert was equally driven in another vein. He preferred to be the administrator. He helped his father create and establish a card-file system that has been the role model for those of other law enforcement entities ever since, including the FBI.

"The offices of the Pinkerton National Detective Agency became a database of criminal activity," declares Pinkerton's Website. "A Pinkerton innovation, the mug shot, soon spread to use among police and other detective organizations. By the 1870s, Pinkerton's had the largest collection of mug shots in the world. As criminals and crimes made the newspapers, field agents diligently clipped and sent in every story with added notations that went into each group's growing file." Folders on criminals would remain in the central files until that person was dead.

The "Pinks," as the nation took to calling the famous lawmen, were everywhere. So fastidious were they in monitoring trends of criminality – even the possible outlet of criminality – the procedures sometimes crinkled the faces of many innocent parties, but frowned the faces of those related to the duplicity. For instance, because the underworld was personally involved in or actually ran illegal horseracing in the latter half of the 1800s, agents made it a habit to check on the certification of every track across America, and the people behind the grandstands. Every racehorse in the country, as it entered the professional circuit, was photographed and described down to its hoof prints so that, if the animal ran a suspect race, Pinkerton could trace it to its owners. Whatever snobbish complaints the turf clubs may have insinuated against what they saw as such insulting behavior, they could not say the sport was entirely clean; bank robbers Jesse and Frank James were known "breeders" of thoroughbreds.

"The Eye" in 1866 (Pinkerton's, Inc.)

Over the years, The Eye himself was often credited with having a third sense, an ability to identify guilty parties of crimes long before police investigators were able to come up with alleged names. He laughed at the notion he had mystic powers, but explained his talent on a simple thing: experience. Each criminal, he told an audience in 1880, has his or her marked, personal technique that gives them away every time: "On reading a telegraphic newspaper report of a large or small robbery, with the aid of my vast records and great personal experience and familiarity with these matters, I can at once tell the character of the work, and then, knowing the names, history, habits, and quite frequently, the rendezvous of men doing that type of work, am able to determine, with almost unerring certainty, not only the very parties who committed the robberies, but also what disposition they are likely to make of their plunder, and at what points they may be hiding."

Pinkerton and his sons, having made the pursuit of criminals a professional business, took their results directly to the business public, educating them on the types of foe they faced. In the 1870s, 80s and 90s, Pinkerton spokespeople, usually William or Robert, offered advice and preventive measures to banks, shipping offices, mail services and other enterprises that dealt with the handling and movement of money. The Pinkerton National Detective Agency became, in sort, a teaching tool for many large city law bureaus who looked upon them as the idyllic tone of law enforcement.

Both police and business kept in touch with Pinkerton for consultation. The communication was a two-way street, for Pinkerton effected a continual flow of information to these entities in forms of wanted posters, mug shots, felons' identification cards and pamphlets for securing such and such a business against break-ins, hold-ups and confidence games.

A Pinkerton-compiled glossary, created in the 1880s, lists terms used by bank and train robbers and their gangs. Reading it, it gives one a colorful ingress into the colloquialism of that seedy inner-society. Following is a partial list of that glossary from the Pinkerton Website:

• Bull                     an officer (of the law)
• Cannon (or Rod) revolver
• Chip                    money drawer (in a bank)
• Dangler               express train
• Ditched               arrested
• Dump                   jail (or boarding house)
• Gay Cat               one who cases banks and towns for future jobs
• Jimmying a bull   shooting an officer
• Mouthpiece         lawyer
• Oil (or Soup)      nitroglycerine (used to open many a bank vault)
• Rattler                 freight train
• Settled                 sentenced to prison
• White Liner         alcoholic
• Yegg (or John Yegg)  bandit chief

*****

In the period following the war, America moved westward.

And so did the criminals.

And so did Pinkerton, to hunt them down.

Remote agency offices opened across the sagebrush trails, from Kansas to California, from Texas to the Canadian border, so that wherever hold-up men tipped a bank, paused a money train or removed an express box from a stagecoach, Pinkerton detectives were a spur-dig away. By this time, Allan Pinkerton had begun to slow with age – physically, not mentally – and William took up much of the frontier legwork. He often conducted posses of agents in search of some of the West's landmark names, Jesse James, Cole Younger, Butch Cassidy and the Sundance Kid, "Black Jack" Tom Ketcham, the Burrow Gang, Hillary Farrington, the Reno brothers and William Randolph.

Between 1865 and the first decade of the 1900s, the Pinkertons directly or indirectly brought to justice every one of them. It was Pinkerton strategy to form an ever-constant, ever widening network of man hunters that could close in, like a noose, on the bad men as they moved through the territory, taunting their every movement, taking away their leisure until, harassed, they panicked and did something stupid under duress to get themselves caught. The wide-open territory the lawbreakers thought they had to hide in became, due to the Pinkertons, a corner in which they found themselves wedged. Even the mention of the name Pinkerton perspired many a desperado's brow.

One of the first to go were the train-robbing Reno clan of six brothers who, after striking an Adams Express car in 1867, never saw a day's rest. More than once they tried to kill William Pinkerton to get his men off their backs. By the end of 1868, all the Renos were dispatched to their graves or in captivity.

William escaped another intent to kill by thief Hillary Farrington. Despite his effeminate name, Hillary was a brute of a thing, a towering, ugly, sadistic gorilla that shot William in the side when cornered on a Kentucky farm. William managed to subdue him, despite his wound, and cuff his wrists. On a paddlewheel boat the following morning en route to Columbus, Kentucky, where the Pinkerton planned to deposit his prisoner, Hillary broke loose from his manacles. Grabbing for the other's shotgun, William managed to hold onto it, but a struggle for the weapon ensued. As they bounced across the deck, knocking over anything or anyone who stood innocently by, the grappling men found themselves in a death fight that led them to the hind-deck of the ship. When the gun inadvertently discharged, a bullet grazed William's skull. In shock, he teetered back, long enough for the killer to wrench it free. But, before Hillary could aim, William recovered long enough to deliver an angry upper-cut that sent the foe spinning backwards over the rail, gun and all, onto the swiftly stirring paddle wheel. Hillary Farrington was chopped to pieces.

Former Civil War guerillas-turned-gunmen Jesse and Frank James found the Pinkertons especially vexing. Their gang's greatest strength was the backing they received by their own southern Missouri populace. Well into the 1870s, many still rankled that the North had won the war and saw their Jesse as a modern-day Robin Hood fighting the wealthy Yankee bankers and rail men tooth and nail. The "Pinks" were considered the tools of the tycoons and met with closed mouths and voodoo eyes when on the trail in those parts. Despite day-to-night manhunts -- rides in which "Old Man Allan" Pinkerton himself often took part -- they continued to lose the James boys in the maze of Smoky Mountain foothills.

The Pinkerton National Detectives, who had a reputation for fair play that even some outlaws admired, rarely faced negative press. But, a scandal erupted that for a short time vilified the agency when, on a warm evening in 1875, two members of the James family were innocently attacked by a Pinkerton-led posse. Believing Jesse was inside, the men surrounded the small cabin near Kearney, Missouri, and demanded that the bandit surrender. When no one answered, someone tossed an explosive through an open window. Zerelda James, Jesse's mother, was maimed and a retarded stepbrother was killed.

Back in Chicago, Allan expressed his deep regrets, but staunchly denied that any of his men had thrown a bomb. His boys were there, he admitted, but had done no more than lay in the underbrush surrounding the cabin and wait in silence for the inhabitants to come out, hands up. That an explosion occurred was doubtless – some historians claim the arsonist had been one of the hired-on deputies – some say that a warning shot from a detective's gun had inadvertently pierced a kerosene lamp inside the house; nevertheless, no one ever accepted the blame, but the agency took it on the chin for some time to come. Jesse later claimed that he had gone to Chicago to kill the Pinkerton chief, but that tale has never been substantiated and scholars have called it hogwash.

When the James' dared to venture from their beloved south to hit a bank as far as Northfield, Minnesota, however, they found a less sympathetic public; in fact, they met with savage resistance. Because the Pinkertons had sent information in advance that the James gang – which also included three of the renegade Younger brothers – was heading north, the town's citizens were ready. Caught in hellish gunfire, the outlaw band withered under tremendous gunfire. Wounded and bloody, Jesse and Frank escaped, but it was the beginning of their end. They had shown vulnerability.

Jesse James died at the hands of one of his own reward-hungry men in April, 1882. Frank, after serving time, lived peaceably thereafter on his farm in Missouri.

Wyoming's Hole-in-the-Wall-Gang had been robbing stagecoach lines and banks for some time when the Pinkertons decided to step in, urged by desperate rail men who were tired of having their boxcar safes blown asunder. One of the reasons for the gang's elusiveness was that after every job they retreated into a mountain fortress whose location still escapes detection by historians. Pinkertons promised quick action – and the public got it.

Butch Cassidy (Pinkerton's, Inc.)

"The gang consisted of (Butch) Cassidy, George 'Flatnose' Curry, Harvey Logan, Lonny Logan, Ben Kilpatrick, the Sundance Kid (Harry Longbaugh or Longabaugh), and Ben Beeson," explains Jay Robert Nash in Western Lawmen & Outlaws. "(In Wyoming) the bandits stopped the Union Pacific's Overland Flyer (and stole) $30,000 in bank notes and securities...This spectacular raid caused the Union Pacific to bring in the Pinkerton Detective Agency, which sent scores of agents after the outlaws."

Pinkerton's men, among them top guns Joe Lefors and Charles Siringo, gave chase. After the wild bunch held up the Great Northern Express near Wagner, Montana, detectives bottlenecked their escape route and cut them off from their familiar Wyoming digs. The gang was forced roundabout south to Fort Worth, where many of them and their accomplices either died fighting or surrendered. Among the bandits' fatalities were the Logans, Harvey and Lonny, Bill Carver, Tom Ketcham, "Flatnose" Curry, "Deaf Charlie" Hanks and Ben Kilpatrick. Self-defined leaders Butch Cassidy and the Sundance Kid made it across the border, from whence they escaped to Bolivia. The South American government refused to extradite the pair back to America but, when the duo began plying their trade of bank robbery there, sent a detachment of its own soldados to gun them down. The troops caught them hiding in the small villa of San Vicente and filled their bodies full of lead.

Before the end of the 19th Century, the Pinkerton agency realized it had survived a chaotic time and had been, in fact, a better part of that bloody era. In demanding the law and in obsessively going after those who didn't, they proved their longevity in the face of death threats and intimidation. Moreover, they proved that they practiced what they preached. And this, their ability to remain honest but tough, had been their most lethal tool.

When reformed safecracker George White wrote a book, From Boniface to Bank Robber, in 1895, he attributed glowing testimony to an old adversary, the Pinkertons. In his pages, he writes: "Strictly speaking, I hated (them) as thoroughly as the corrupt police did because of their interference with my professional duties. Many a time I had been enraged and beaten out of thousands by the popping up of one or more of the agency's men.

"Nevertheless, I had to acknowledge that they were honest and it was dangerous for a crook when a Pinkerton was on his trail."