As aristeides pointed out, it all began after the Ari remark about a single bullet taking out Saddam Hussein.
Yes, this has been one of the things that has suggested terrorism all along. (To give credit, I first saw the idea in an Oct. 11 post by okie01.)
It was on Oct. 1 that Ari Fleischer suggested assassinating Saddam Hussein with a "single bullet." It was the very next day, Oct. 2, that the DC sniper killed his first victim.
The official transcript of the Oct. 1 Ari Fleischer press briefing can be found at this link.