After leaving the military, Trudell had become involved in Indian activism. In 1969, he became the spokesperson for the United Indians of All Tribes' occupation of Alcatraz Island. This was a mostly student-member group that had developed in San Francisco. Trudell went to Alcatraz a week after the occupation started. He used his background in broadcasting and ran a radio station from the island through a cooperative arrangement with students at the University of California, Berkeley, broadcasting at night over the Berkeley FM station. The show was called Radio Free Alcatraz. He discussed the cause of the occupation and American Indian issues, and played traditional Native American music. He criticized how "the system today is only geared toward white needs. " He spoke for the many Indians who believed they did not fit in with the then majority European-American population of the nation. He became a spokesperson for the occupation specifically and for the Alcatraz-Red Power Movement generally, as the author Vine Deloria, Jr. named it. Trudell was the spokesman for the nearly two-year-long occupation, until 1971.