I suspect from the psychotherapist the criminal psychiatrist from the first moment.
What might happened is he had a trauma and he forget his memories, I believe he has a twin or someone pretending to be him wearing a mask of him, we even saw this happening in historical dramas, we had it Mission Impossible way back when it was a TV Drama in early 1990 late 1980's.
Hypnosis is quite possible, drugging is also quite possible. For drugging if it is drugging someone in his close circle is doing it, and it also needs to continue in his prison cell..
For the framing I suspect from the chief he is related that's what I am guessing not everyone is as honest as him