Kudos, Rich. You are correct. In later years Withers stated, "It was mainly on my testimony that the principals in the case were convicted." Withers made a series of embellished or untrue statements including maintaining that Tad Lincoln was in the box with his parents that night.
Tom Bogar mentions Withers' statement here. Scroll to 6:25 of the video.
"Let me no the truth about this murder of the Chief President....I want to no wat you no about it....My hand is so lame that I can scarcely hold the pen...."