Speed was appointed as a special prosecutor on April 11, 1898 to investigate the lynching of two Seminole Indian boys who had been accused of the rape and murder of a white woman and her baby. A mob of vigilantes had captured the boys, chained them to a tree and burned them to death. Speed's investigation identified the perpetrators and resulted in the arrest, conviction and sentencing of 45 white men for kidnapping and 45 for arson. It was the first time lynchers had been convicted in the Southwest.