The FBI is notorious for not releasing information on active cases unless there is a compelling reason. Local Law Enforcement is more subject to political pressure. They might release information in order to reassure the public that the case is moving forwards.
The FBI can only take jurisdiction if a case meets certain criteria (such as kidnapping for ransom, terrorism, interstate crimes etc.) but they can assist local Law Enforcement under other circumstances. In thoseIIRC situations, the Locals would maintain jurisdiction and would have discretion on releasing information.
IIRC, there are quotes in the book that say that the BCA and FBI are still involved.
The BCA is the one who found info that got sealed search warrants to search the farm in 2010. They go through cold cases looking at info with new eyes.