Someone found the snake near their house and killed it.
From The AJC:
Zoo spokeswoman Keisha Hines said Sunday the nocturnal snake was believed to be still inside the building where it was housed, which is not accessible to the public. But Hines could not say why staff thought the snake was still in that building. Hines said signs warning the public were not needed.Yeah, hindsight. That's what it takes. No one could be expected to figure that out using foresight.
"Hindsight being 20/20, we probably should've knocked on a few doors," (Zoo Atlanta deputy director Dwight) Lawson said. The local neighborhood association was alerted, he said, and an announcement was made to visitors at the zoo Saturday, he said, though there was no follow-up announcement Sunday.
Update: In hindsight, I've changed my mind. I mean, it was in the newspaper - albeit with the caveat of "We think it's in this building ... although we can't find it or tell you why we think that."
So let this be a lesson to you: Read the newspaper, or a rattlesnake might kill one of your children.