<P> The massacre was allegedly planned by the organization led by Al Capone to eliminate George `` Bugs '' Moran , the boss of the long - established North Side Gang . The former boss of the North Side Gang , Dean O'Banion , had been murdered by four gunmen in his flower shop on North State Street in 1924 . After the murder of O'Banion , each successive leader of the North Siders was also killed , allegedly by various members or associates of the Capone organization . </P>
who ordered the st valentine 's day massacre
allegedly planned by the organization led by Al Capone