George Leonidas Leslie led a double life: By day, he was a distinguished architect who hobnobbed with New York City's elite denizens; by night, he was one of history's most prolific bank robbers.

Unlike other heisters of his time, Leslie's approach was academic rather than brutish. He studied the anatomy of locks, drafted up blueprints of banks, and invented mechanical safe-breaking devices.

During his authorities estimated that his exploits accounted for 80% of all bank robberies in the entire US during his active years of 1869-78.

Altogether, he stole at least $7m ($200m in today's money), much of it pilfered from the bank vaults of America's wealthiest titans.

He took up residence at the prestigious Fifth Avenue Hotel - a gathering place for the ultra-elite of the Gilded Age, including shipping and railroad tycoon Cornelius Vanderbilt and then-president Ulysses S. Grant.

Though he wasn't a millionaire himself, Leslie ingratiated himself into the high-status world, donning the finest suits, attending theater openings, and collecting rare books.

His apparent wealth and pedigree gained him the friendship of robber barons like Jim Fisk (a millionaire who cornered the gold market and orchestrated Black Friday), Jay Gould (a railroad magnate), and Tweed (a corrupt politician who embezzled millions from taxpayers).

These men, and other members of high society, saw Leslie as a bon vivant of the highest order and accepted him with open arms.

But Leslie had an ulterior motive.

Robbing banks wasn't exactly the kind of profession one could learn from books. It required a strong connection to the criminal underworld. And he found just that in a woman named Fredericka Mandelbaum.

Mandelbaum was New York's greatest

Working with an expansive band of criminals and pickpockets across the city, she housed and resold millions of dollars of stolen goods - largely with impunity. Like Leslie, she was with the elites, whom she hosted at extravagant parties in a home appointed with ill-gotten luxuries.

Introduced through Fisk, Leslie and Mandelbaum hit it off in grand fashion.

Leslie selected his first target - Ocean National Bank in New York City - and began a laborious, three-month-long planning process.

In June 1869, Leslie made his move.

First, the planted employee let him in at night, after the guards had gone, and he installed his little joker device, a tiny tin wheel with a metal wire around it that went behind the combination knob of the vault's lock.

When the tellers used the vault the next day, the little joker, hidden behind the dial, would get etched with deep cuts where the three numbers of the code were, limiting the combination to just a few possibilities.

Several nights later, Leslie and his crew entered the bank again, removed the little joker, and used the etches to crack the lock.

This only gained them entry through the first door: The safe had three of them, each built of thick iron. And inside the vault the safes had to be opened, too.

For this, the crew relied on a bevy of tools - jimmies, wedges, sledges, nippers, and drills.

The following morning, bank officials arrived at a chaotic scene: floors strewn with coins, bank notes, and drill bits. But the main door to the vault was intact, which stumped investigating police officers.

The New York Herald declared it A report in The New York Times remarked that a robbery of this type was

In sum, Leslie and his crew made off with $768,879.74 (~$27.5m today) - a record-setting sum.

And that was just the beginning.

For more information on the book, see:
King of Heists: The Sensational Bank Robbery of 1878 That Shocked America(https://www.amazon.com/King-Heists-Sensational-Robbery-Shocked/dp/1599215381/ref=sr_1_1)

To read the complete article, see:
The architect who became the king of bank robberies(https://thehustle.co/the-architect-who-became-the-king-of-bank-robberies/)