The most crucial piece of evidence presented at Blanton's trial was an audio recording secretly taped by the FBI in June 1964, in which Blanton was recorded discussing his involvement in the bombing with his wife, who can be heard accusing her husband of conducting an affair with a woman named Waylen Vaughn two nights before the bombing. Although sections of the recording—presented in evidence on April 27—are unintelligible, Blanton can twice be heard mentioning the phrase "plan a bomb" or "plan the bomb". Most crucially, Blanton can also be heard saying that he was not with Miss Vaughn but, two nights before the bombing, was at a meeting with other Klansmen on a bridge above the Cahaba River. He said: "You've got to have a meeting to plan a bomb."