As SonnyD pointed out, Capone was connected to the Masseria clan. Theres also a story that after the murder of Masseria, Maranzano was planning to kill Capone also and so the young turks made an example of Maranzano.

During the Castellammarese conflict Paul Ricca was sort of a “peacemaker” between the warring factions but secretly the Capone gang “supported” the Masseria clan.It was the era of backstabbing games.The Eastern mob found Ricca to be very responsive to their desires to connect with the otherwise isolated Chicago mob.They saw Ricca as a very secretive and shrewd mobster.After the deaths of Masseria and Maranzao, Luciano and Lansky had a big meeting in Chicago with Ricca and Agoglia who was an ex-NY mobster and close confidant of Ricca.