The BOI and local police investigated the case for over three years without success. Occasional arrests garnered headlines but each time they failed to support indictments. Most of the initial investigation focused on anarchists and communists, such as the Galleanist group, whom authorities believed were involved in the 1919 bombings. During President Warren G. Harding's administration, officials evaluated the Soviets and the Communist Party USA as possible masterminds of the bombing. In 1944, the FBI, successor to the BOI, investigated again. It concluded that its agents had explored many radical groups, "such as the Union of Russian Workers, the I.W.W., Communist, etc. ... and from the result of the investigations to date it would appear that none of the aforementioned organizations had any hand in the matter and that the explosion was the work of either Italian anarchists or Italian terrorists."