No. of Recommendations: 3
Suppose they lawfully break into your house or your phone, and thereby discover a video or written testimonial you made attesting to some specific thing about the "contents of your mind" that incriminates you in some way. Can that then be used against you?
Of course. Any documents or other evidence that they obtain lawfully is admissible. You can't be compelled to be a witness against yourself, but your papers or recordings can certainly be entered into evidence, if obtained lawfully. If you write out a confession to crimes in your diary (for example), you can't use the Fifth Amendment to keep the government from using that.
