Was Vegas shooter ranting about Waco, Ruby Ridge, FEMA camps?
Sourcing is thin, and wouldn't the government just love to have a mass shooting they could blame on people opposed to gun control? The targeting doesn't make any sense, either.
I don't buy this one, whether it was mistaken identification or a jailhouse source making things up.
Worst-case scenario: the man doing the ranting about Waco was an FBI agent or informant, per .. well... per Ruby Ridge and the Draw Mohammad attack and the Oaklahoma City bombing. Under that hypothesis, the FBI (or some other government agency) had been tipped off to the alleged shooter, had an informant or agent there with him, and ranted at him in public. That seems a horribly unlikely scenario if they knew he was planning a mass murder in three days, but if they just got a tip and are trying to interrogate him under cover with an informant, it becomes more plausible. And, of course, admitting they were that close but did not act becomes an embarrassment after the fact, something worth covering up.