The Tremas Master sent Melanie Bush and Sabalom Glitz to Space Station Zenobia to act as witnesses in the Sixth Doctor's trial. (TV: The Ultimate Foe)
Leela, K9 Mark I (who also spoke for K9 Mark II), Narvin and Torvald were witnesses at the inquiry into Romana II's actions on Gryben. (AUDIO: The Inquiry)
Eye witnesses claimed to have seen an angelic woman emerge from the wreck of the Elysium on 17 July 1888, according to later documentation in the 2010s. (PROSE: Pride of Mayfield Star Lines Beached in Devastating Storm)
Other contexts
During the Year That Never Was, the Saxon Master deemed that the Tenth Doctor should be a witness for when he killed Martha Jones. (TV: Lat of the Time Lords)
Davros intended for the Doctor and the Children of Time to witness the detonation of the Reality bomb. (TV: Journey's End)