http://sadbastards.wordpress.com/2007/05/09/sirhan-sirhan-fired-the-first-deadly-shot-in-our-war-with-islamic-terrorisim/
http://www.nndb.com/people/580/000024508/
One of these articles says he was Christian, the other says he was a member of the PLO working under orders of Arafat.
I dont know about PLO I do know about POS and he qualifies.
There is no contradiction between Sirhan Sirhan being PLO and an Arab Christian (albeit a bad one, since good Christians don’t murder folks). The PLO included the PFLP, headed by George Habash (at least a nominal Christian). Arafat’s wife was a Christian.
Until the past decade or so when all Arab militant groups took on a jihadi aspect, the PLO was principally a secularist nationalist movement, along the lines of the Ba’athist regimes in Syria and Iraq, and quite cozy with the Soviets back during the Cold War.