He said it as a joke?

Haggai Amir threated PM Sharon's life from prison.
He claims he said it as a joke. Is he nuts? Considering who his brother is and what he is sitting in jail for (even if you have questions regarding the assassination that only Barry Chamish deals with), Haggai Amir claims he threatened a PM's life as a joke??!! He would be better off pleading insanity now..