If the following can be believed, he was apparently a Christian when he was younger.
We missed him. Our chance to change things came and passed and we did not know it was there. A dark-skinned little boy sat through Sunday School classes for three years at a great Baptist Church (First Church, San Antonio) but some one missed him. His name was Sirhan Sirhan, and at age 24 he shot and killed Senator Robert Kennedy. In a welter of words and the shudder of grief throughout our nation, the persistent thought keeps recurring...someone missed him.
Dr. Jimmy Allen, former pastor of First Baptist Chruch, San Antonio, Texas in Pulpit Helps, May, 1991.
http://www.christianglobe.com/Illustrations/theDetails.asp?whichOne=o&whichFile=opportunity
And then there is Daniel Pipes, at:
http://www.danielpipes.org/comments/1928
Sirhan Bishara Sirhan, born March 19, 1944, in Jerusalem, is a Christian, not a Muslim.