* Murder: Siegel was suspected of involvement in several murders, including the 1931 killing of Harry Greenberg and the 1941 killing of Benjamin "Bugsy" Siegel.
* Tax evasion: Siegel was convicted of tax evasion in 1944 and served a one-year sentence in federal prison.
* Illegal gambling: Siegel was involved in illegal gambling operations in Las Vegas, including the Flamingo Hotel and Casino. He was forced out of the Flamingo by organized crime figures in 1947.