Yes, he did in his recently unearthed book he co-authored with Bernardine Dorhn amongst others. It is called Prairie Fire, The Politics of Revolutionary Anti-Imperialism. They dedicated the book to all American political prisoners including the Palestinian murderer of Senator Robert Kennedy, Sirhan Sirhan.

One wonders if Obama's Kennedy family supporters really care or, perhaps, they were too young when the atrocity happened?

Zombie Time has best discussion of the book including some pages from it.