Delphine Roberts worked for Guy Banister and later became his mistress. Roberts told Anthony Summers that during the summer of 1963 Lee Harvey Oswald worked for Banister.

On the afternoon of 22nd November, 1963, Banister and Jack Martin went drinking together. On their return to Banister's office the two men got involved in a dispute about a missing file. Banister became so angry that he he drew his Magnum revolver and hit Martin with it several times. Martin was so badly injured that he had to be detained in the local Charity Hospital.

Over the next few days Martin told friends that Guy Banister and David Ferrie had been involved in the assassination of John F. Kennedy. According to Martin, Ferrie was the getaway man whose job it was to fly the assassin out of Texas. He also claimed that Ferrie knew Lee Harvey Oswald from their days in the New Orleans Civil Air Patrol and had given him lessons on how to use a rifle with a telescopic sight.

On 25th November, Martin was contacted by the Federal Bureau of Investigation. He told them that he thought Ferrie had hypnotized Oswald into assassinating Kennedy. The FBI considered Martin's evidence unreliable and decided not to investigate Banister and Ferrie.

This information eventually reached Jim Garrison, the district attorney of New Orleans. He interviewed Martin about these accusations. Martin claimed that during the summer of 1963 Banister and David Ferrie were involved in something very sinister with a group of Cuban exiles.

Jim Garrison now became convinced that a group of right-wing activists, including Guy Banister, David Ferrie, Carlos Bringuier and Clay Shaw, were involved in a conspiracy with the CIA to kill John F. Kennedy.

Roberts said she was in the office when Banister suggested that Lee Harvey Oswald should establish a local Fair Play for Cuba Committee. This story was supported by her daughter who met Oswald during this period.