“The inescapable fact is that the men deserved a second trial.” Bruce Watson writing in the Wall Street Journal, “The Unending Trial of Sacco and Vanzetti: A century ago, the murder conviction of two Italian immigrants set off a worldwide protest movement and revealed a polarized America.”
Here is the very good Wikipedia entry on the case.
Both men belonged to Gruppo Autonomo, an anarchist group in East Boston
The noted muckraker Upton Sinclair thought the pair was guilty. The historian Francis Russell thought Sacco guilty and Vanzetti innocent.