Ferguson is charged with defaming the city's pension board.
Tait told the courtroom Ferguson never showed concrete proof of illegal activity by the board, even after getting the chance to lay out his entire case during an open session of council.
Tait, who was also a pension trustee, said he was affected by the allegations because people could have assumed he was Ferguson's inside source on the shady activity.
Ferguson said he knows the "name, rank, and serial number" of the source and Tait held the rank of Fire Chief.
There will be no testimony tomorrow as the jury will be using the day to go over the vast volumes of documents in the case.
