That document doesn't say that the FBI was trying to assassinate the Occupy Houston leaders. It says the FBI uncovered some other party's plot (apparently, organized crime) to do that. Ryan Shapiro sued to find who the snipers were but was eventually denied. http://www.courthousenews.com/2015/02/06/fbi-gets-ok-on-alle...
See the article linked at the end of my previous post:
> The FBI was right to withhold records about an alleged murder plot targeting the leaders of Occupy Houston, to protect its informants, a federal judge ruled.