In his early twenties, Capone moved to Chicago and became a bodyguard of Johnny Torrio, head of a criminal syndicate that illegally supplied alcohol—the forerunner of the Outfit—and was politically protected through the Unione Siciliana.

Although Capone expanded the bootlegging business through increasingly violent means, his mutually profitable relationships with Mayor William Hale Thompson and the Chicago Police Department meant he seemed safe from law enforcement.

[8] Ralph ran Al's bottling companies (both legal and illegal) early on and was also the front man for the Chicago Outfit until he was imprisoned for tax evasion in 1932.

During this time he was employed and mentored by fellow racketeer Frankie Yale, a bartender in a Coney Island dance hall and saloon called the Harvard Inn.

[23] In 1919, Capone left New York City for Chicago at the invitation of Torrio, who was imported by crime boss James "Big Jim" Colosimo as an enforcer.

After recovering, he effectively resigned and handed control over to Capone, aged 26, who became the new boss of an organization that took in illegal breweries and a transportation network that reached to Canada, with political and law-enforcement protection.

An infuriated Joe Aiello, who had wanted the position himself, believed Capone was responsible for Lombardo's ascension and resented the non-Sicilian's attempts to manipulate affairs within the Unione.

[55] Chicago politicians had long been associated with questionable methods, and even newspaper circulation "wars", but the need for bootleggers to have protection in city hall introduced a far more serious level of violence and graft.

Capone is generally seen as having an appreciable effect in bringing about the victory of Republican mayoral candidate William Hale Thompson, who had campaigned on a platform of not enforcing Prohibition and at one time hinted that he'd reopen illegal saloons.

[57][58] On the day of the Pineapple Primary on April 10, 1928, voting booths were targeted by Capone's bomber, James Belcastro, in wards where Thompson's opponents were thought to have support, causing the deaths of at least fifteen people.

Belcastro was accused of murdering lawyer Octavius Granady, an African-American, who challenged Thompson's candidate for the Black vote, and was chased through the streets on polling day by cars of gunmen before being shot dead.

[65] The massacre was an attempt to eliminate Bugs Moran, head of the North Side Gang, and the motivation for the plan may have been the fact that some expensive whisky that was illegally imported from Canada via the Detroit River had been hijacked while it was being transported to Cook County, Illinois.

[66] Moran was the last survivor of the North Side gunmen; his succession had come about because his similarly aggressive predecessors, Weiss and Vincent Drucci, had been killed in the violence that followed the murder of original leader Dean O'Banion.

[67][68] To monitor their targets' habits and movements, Capone's men rented an apartment across from the trucking warehouse and garage at 2122 North Clark Street, which served as Moran's headquarters.

Within days, Capone received a summons to testify before a Chicago grand jury on charges of federal Prohibition violations, but he claimed to be too unwell to attend.

[72][2] The Saint Valentine's Day Massacre led to public outcry about Thompson's alliance with Capone, and this was a factor in Anton J. Cermak winning the mayoral election on April 6, 1931.

[75][76] Bair questioned why "three trained killers could sit quietly and let this happen", while Hazelgrove stated that Capone would have been "hard pressed to beat three men to death with a baseball bat" and that he would have instead let an enforcer perform the murders;[75][76] however, despite claims that the story was first reported by author Walter Noble Burns in his 1931 book The One-Way Ride: The Red Trail of Chicago Gangland from Prohibition to Jake Lingle,[75] Capone biographers Max Allan Collins and A. Brad Schwartz have found versions of the story in press coverage shortly after the crime.

Collins and Schwartz suggest that similarities among reported versions of the story indicate a basis in truth and that the Outfit deliberately spread the tale to enhance Capone's fearsome reputation.

Treasury and Justice Departments developed plans for income tax prosecutions against Chicago gangsters, and a small, elite squad of Prohibition Bureau agents (whose members included Eliot Ness) were deployed against bootleggers.

[84] On March 27, 1929, Capone was arrested by FBI agents as he left a Chicago courtroom after testifying to a grand jury that was investigating violations of federal prohibition laws.

[93] U.S. Assistant Attorney General Mabel Walker Willebrandt is said to have originated the tactic of charging obviously wealthy crime figures with federal tax evasion on the basis of their luxurious lifestyles.

[77]: 385–421, 493–496 [98][97] On June 16, 1931, at the Chicago Federal Building in the courtroom of Wilkerson, Capone pleaded guilty to income tax evasion and the 5,000 Volstead Act violations as part of a 2+1⁄2-year prison sentence plea bargain.

Capone's lawyers, who had relied on the plea bargain Wilkerson refused to honor, therefore had mere hours to prepare for the trial, ran a weak defense focused on claiming that essentially all his income was lost to gambling.

He was seen as a weak personality, and so out of his depth dealing with bullying at the hands of fellow inmates that his cellmate, seasoned convict Red Rudensky, feared that Capone would have a breakdown.

No solid evidence ever emerged, but it formed part of the rationale for moving Capone to the recently opened Alcatraz Federal Penitentiary off the coast of San Francisco, in August 1934.

[115] Due to his good behavior, Capone was permitted to play banjo in the Alcatraz prison band, the Rock Islanders, which gave regular Sunday concerts for other inmates.

[117] At Alcatraz, Capone's decline became increasingly evident, as neurosyphilis progressively eroded his mental faculties; his formal diagnosis of syphilis of the brain was made in February 1938.

[119] Capone completed his term in Alcatraz on January 6, 1939, and was transferred to the Federal Correctional Institution at Terminal Island in California to serve out his sentence for contempt of court.

Organized crime in the city had a lower profile once Prohibition was repealed, already wary of attention after seeing Capone's notoriety bring him down, to the extent that there is a lack of consensus among writers about who was actually in control and who was a figurehead "front boss".

[127][better source needed] After a few weeks of inpatient and outpatient care, on March 20, 1940, a very sickly Capone left Baltimore and travelled to his mansion in Palm Island, Florida.