The Big O aired On Toonami throughout April of 2001, and shortly reran afterwards. The series, (like most anime aired on Toonami during this time) was edited for content. From edits that removed blood, violence, and religious references, most notably changing the phrase "Cast In The Name Of God, Ye Not Guilty" to "Cast In The Name Of Good, Ye Not Guilty".
However, these edits have only appeared on Toonami's broadcasts of the show, as further broadcasts would air on [adult swim] uncut. And all DVD/Blu-Ray releases of the show are uncut as well, there was never a VHS release (which is where toomami edits of other anime series such as DBZ could be found). And no footage online of the actual edits exist, as the only way I was able to find out about these edits were these links: