Amnesia was not a defence in a court of law. (TV: The Bounty Hunter [+]Loading...["The Bounty Hunter (TV story)"])
The Valeyard believed that the Sixth Doctor was attempting to use amnesia as a defence during his trial. The Doctor confirmed that this was not the case. (TV: Mindwarp [+]Loading...["Mindwarp (TV story)"]) When it came time for him to respond to the Valeyard's case, he made it clear that his defence was that his behaviour would improve. (TV: Terror of the Vervoids [+]Loading...["Terror of the Vervoids (TV story)"])