In 1946, Lansky convinced the Italian-American Mafia to place Siegel in charge of Las Vegas, and became a major investor in Siegel's Flamingo Hotel. To protect himself from the type of prosecution which sent Al Capone to prison for tax evasion and prostitution, Lansky transferred the illegal earnings from his growing casino empire to a Swiss bank account, where anonymity was assured by the 1934 Swiss Banking Act. Lansky eventually even bought an offshore bank in Switzerland, which he used to launder money through a network of shell and holding companies.
Lansky attended a secret meeting in Havana in 1946 to discuss Siegel's management of the Flamingo Hotel, which was running far behind schedule and costing Siegel's Mafia investors a great deal of money. While the other bosses wanted to kill Siegel, Lansky begged them to give his friend a second chance. Despite this reprieve, Siegel continued to lose money on the Flamingo. A second meeting was then called. However, by the time this meeting took place, the casino turned a small profit. Lansky again, with Luciano's support, convinced the other investors to give Siegel some more time. However, when the hotel started losing money again, the other investors decided that Siegel was finished. It is widely believed that Lansky himself was compelled to give the final okay on eliminating Siegel due to his long relationship with him and his stature in the organization.
The Havana Conference was held on December 22, 1946, at the Hotel Nacional. This was the first full-scale meeting of American underworld leaders since the Chicago meeting in 1932. Present were such figures as Joe Adonis, Albert "The Mad Hatter" Anastasia, Frank Costello, Joseph "Joe Bananas" Bonanno, Vito Genovese, Moe Dalitz, Thomas Luchese, from New York; Santo Trafficante Jr. from Tampa; Carlos Marcello from New Orleans; and Stefano Magaddino, Bonanno's cousin from Buffalo. From Chicago there were Accardo and the Fischetti brothers, "Trigger-Happy" Charlie and Rocco; and, representing the Jewish interest, Lansky, Dalitz and "Dandy" Phil Kastel from Florida.