During the early 1940s, Flores joined activists, lawyers, writers, and citizens to form the Sleepy Lagoon Defense Committee.
Their goal was to free a group of young Mexican Americans who had been convicted of the muder of Jose Gallardo Diaz in 1942. The trial, which was the largest mass murder trial in California history, had been marred by a lack of evidence, coerced testimony, judicial misconduct, deprivation of counsel, and a widespread public assumption that the defendants were criminals and gang members. As a member of the SLDC, Flores interviewed community members, friends, and family of the young men and published passionate editorials arguing against their conviction. Assisted by the combined efforts of the committee and community members, the convictions were thrown out and the young men were freed in 1944.
Defendant Robert Telles and family at the Sleepy Lagoon murder case acquittal, 1944, Herald Examiner Collection, Los Angeles Public Library