Jack Harkness remarked that an unconvincing suicide note was found at the scene of Sam Hallett's suicide. (AUDIO: The Conspiracy)
The Fifth Doctor did not find a note in Sebastian Callow's accommodation after finding him unconscious due to gas. Because of this and the door being locked from the inside, the Doctor deduced that what happened was not self-inflicted. (AUDIO: The Merfolk Murders [+]Loading...["The Merfolk Murders (audio story)"])