One of the more gruesome tales coming in the aftermath of the storm was the claim that 22 dead people tied to a rope had been spotted in Violet, which is in St. Bernard Parish. It wasn't a case of just a really long rope: it was a tall tale. "Officials debunk one of the most disturbing Katrina stories" has the details, and they appear to have found the injection point:
[St. Bernard Parish Fire Chief Tom Stone] said that a resident of the affluent Jumonville subdivision, near Violet, who evacuated during the height of the storm surge told a rescuer that he saw people roped together.
Another story of mass death in the parish around the same time was quickly defused after a local congressman retracted his statement that 100 rescued people had died in a warehouse awaiting evacuation.
While I'm inclined to think some of the horror stories were actually true and conflicted parties are now trying to fool us twice, I'll put these in the "fully debunked" category.