I saw the original post on Craigslist when it was still there. So cannot say with certainty that it was legitimate, but I can confirm that it did exist.
It has since been taken down.
I have come to believing that to expose preparations like this or publishing possible ritualistic/numerologic target dates, can seriously help preventing those evil events from actually happening.
Publicly exposing the evil plans makes it more and more impossible to actually pull those things off.