Character mistake: When Garrison is leaving the house to question Clay Shaw on Easter Sunday, his wife is complaining about his working on the Sunday, and at one point calls Garrison 'Clay'.
Character mistake: Jim Garrison and Lou Ivon are discussing the shooting at the book depository and Jim refers to "our friend Clay Shaw" as having introduced General Charles Cavill at the Foreign Policy Commission in New Orleans. However, Garrison does not find out that Clay Bertrand is Clay Shaw until Bill Broussard finds out from his informant and tells Jim in later scenes. (01:18:54)
Answer: Lee Harvey Oswald was very sympathetic to the communist ideal, and lived in Russia for a while. He probably adopted the accent as an affectation towards that end.
Grumpy Scot