The 1920s was with the party atmosphere it was certainly a time of great criminal activity, with the prohibition laws in America and the world in an economic depression.
In 1920 crimes where so high because the depression was going on and people needed to provide for there family. Thats one reason why people would have to hustle for there money, another reason is because jobs where so hard to get people basically had to do anything they could to live even if it meant they took someone else life. I'm not saying its right because its not but you gotta do what you gotta do.
Sacco & Vanszetti were charged with executing a robbery and murder in exchange for money.
While there was little evidence against the two, the pair were vocal about their anarchist views. They were sentenced to death. They still caught the people who where committing crimes there was just so much going around.