Sacco and Vanzetti were part of an Anarchist gang led by Mike Boda (Mario Buda.) Here is a part of the story that often gets left out...
“The Wall Street bombing occurred at 12:01 pm on Thursday, September 16, 1920, in the Financial District of New York City. The blast killed 30 people immediately, and another eight died later of wounds sustained in the blast. There were 143 seriously injured, and the total number of injured was in the hundreds....
... flyers found in a post office box in the Wall Street area just before the explosion. Printed in red ink on white paper, they said: “Remember, we will not tolerate any longer. Free the political prisoners, or it will be sure death for all of you....”
...One Galleanist in particular, Mario Buda (1884–1963), an associate of Sacco and Vanzetti, and the owner of a car which led to the arrest of the latter for a separate robbery and murder, is alleged by some historians, including Paul Avrich, to be the man most likely to have planted the bomb. Avrich and other historians theorize that Buda acted in revenge for the arrest and indictment of his fellow Galleanists, Sacco and Vanzetti.Buda’s involvement as the Wall Street bombmaker was confirmed by statements made by his nephew Frank Maffi and fellow anarchist Charles Poggi, who interviewed Buda in Savignano, Italy, in 1955...”
https://en.wikipedia.org/wiki/Wall_Street_bombing
Admittedly, there was never a conviction in this case, but I think it’s a mistake to ignore it.
According to the late historian Francis Russell, Buda later returned to Italy and worked in Mussolini’s security apparatus, rising to high rank in the Italian Fascist government.