As the freight train whisked its way over the Alabama rails in 1931, nine boys’ lives were changed forever. The details of their skirmish with a group of white men and two women on the train are still unclear. But by the end of the train ride, nine young men—all African American, all teenagers—were headed toward their death by an unjust, vigilante mob and a legal system that didn’t value their lives.

They were the Scottsboro Boys, and their trial, death sentences, and dramatic appeals helped expose the injustice of the American legal system during the 1930s. But false testimony and rousing pleas for their release weren’t the only drama that surrounded their legal struggle. The Scottsboro case also pitted the NAACP against the Communist Party in a struggle for who would control the boys’ legal defense—and claim this rare spotlight on race in America.

The boys’ case seemed hopeless. After the fight on the freight train, they were falsely accused of rape by the two white women in the group. They were immediately arrested by a posse, thrown into jail in Gadsden, Alabama, and threatened by a lynch mob. Then, all but one were swiftly convicted by all-white juries and sentenced to death.

At this point, an unlikely ally swooped in to mobilize on their behalf: the American Communist Party. At the time, the party was working to make inroads in the United States. Legal advocacy was a critical part of that strategy, and International Labor Defense, the party’s legal defense arm, specialized in offering free legal representation in high-profile cases, like that of Nicola Sacco and Bartolomeo Vanzetti, two Italian anarchists who were tried and ultimately executed for murder and robbery in 1927. The group also took on labor disputes and free speech cases.

Civil rights were a cornerstone of the Communist Party’s platform in the U.S., and the party actively courted black intellectuals and leaders in an attempt to appeal to African-Americans. Throughout the 1920s and 1930s, the ILD began to tackle prominent cases related to lynching, the KKK and other racially motivated crimes. These cases helped make the party more palatable to marginalized groups who traditionally lacked the financial and social resources to defend themselves in court.

And when the Scottsboro case emerged, the ILD saw an opportunity not just to fight for racial equality, but to take advantage of the national spotlight and further their cause.

Lynch mobs and vigilante “justice” were common in the Jim Crow South, which regularly punished black men without cause, and many cases of false accusations and unjust convictions occurred without fanfare or coverage. But the Scottsboro cases couldn’t have been more different. The ILD organized marches, meetings, speeches and letter writing campaigns on the boys’ behalf and launched a full-scale public relations blitz.

However, another influential organization was notably absent from the public defense: the NAACP. This drew a firestorm of criticism from onlookers who wondered why the group—the largest, most well respected and influential African-American advocacy group in the nation—didn’t stand up for the Scottsboro Boys.

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Despite its commitment to fighting for equal rights for African-Americans, the NAACP shied away from cases where a black man was accused of raping a white woman. At the time, the group also had financial issues, and historians like James R. Acker believe it hesitated to get involved in an appeal, either because its leadership doubted the innocence of the boys or because of a mistaken assumption that the boys already had high-quality attorneys in the case.

But Walter White, the NAACP’s head, worried that the Communists wanted to “make martyrs” of the boys for their own gain, and eventually the group decided to vie with the ILD to defend them.

The NAACP reached out to the parents of the Scottsboro boys and offered Clarence Darrow, the formidable attorney who eloquently defended John Scopes’ right to teach evolution in Tennessee schools in the Scopes “Monkey Trial,” and Arthur Garfield Hays, the cofounder of the ACLU, to represent them in their appeal.

In public, the ILD said it welcomed Darrow’s contribution to the case, but in private they leaned on the Scottsboro parents to let them represent them instead. All of the boys signed on with the ILD, and Darrow and Hays withdrew from the case with bitter words. The perception was that the NAACP had faltered at a time when they should have stood behind the Scottsboro Boys.

“I don’t care whether they are Reds, Greens, or Blues,” said Janie Patterson, mother of 18-year-old Haywood Patterson. “They are the only ones who put up a fight to save these boys and I am with them to the end.”

The ILD won their appeal on behalf of the Scottsboro Boys after fighting it all the way to the U.S. Supreme Court, which threw out their convictions. This success was short-lived, however. The teenagers were soon re-indicted on different charges and tried again in Alabama. This time, the Communists and the NAACP came together with the ACLU and other organizations to form the Scottsboro Defense Committee.

Though this legal supergroup managed to sidestep the death penalty for all nine defendants, they didn’t succeed in all nine cases. It would take nearly 20 years before all of the Scottsboro Boys—now men who had undergone multiple trials and served years in the criminal justice system for crimes they did not commit—were released from prison.

The NAACP may have joined with the Communists to help the Scottsboro Boys, but internally they spent years trying to prove that they didn’t sympathize with the Communist cause. During the 1950s, they rooted out Communist members and even helped J. Edgar Hoover as he put together his blacklist and pursued suspected Communists during the Red Scare.

In an age of bias and discrimination, NAACP’s leaders worried that they’d be destroyed if they associated with Communism.  Meanwhile, American Communists turned their eyes toward other struggles. Their rare moment of collaboration proved almost as fleeting as the train ride that changed the lives of the Scottsboro Boys forever.

READ MORE: A Timeline of Black History Milestones