Due to the pressure brought to bare on Mr. Frazier by the Dallas Police some parts of his affidavit could easily have been misleading. He could've easily been told by his sister to make sure he distances himself from the evidence or any knowledge of the contents of the sack,due to the attitude of the Police.Hence the misidentification of the sack and saying he never saw Oswald after the murder.
Mr.Frazier wasn't lying to deceive, he was lying because he was scared out of his wits...and who can blame him the way he was treated by the Police.