A) This is SOURCES SAID "The FBI is desperate.". Sources can say the sky is orange and it doesn't make it true. IMO (maybe the sky is orange, what do I know?)
B)This statement isn't even true. FBI does not just take over a case from local authorities
Does the FBI take over the Investigation. It doesn't matter if the family asks or not. I mean, they can ask if they want, but it's not going to matter.
IMO, Pima county wants to maintain control of the investigation. FBI is trying to help. Some local authorities say "Here, FBI, you do it." but this doesn't seem to be one of those locales. There is so much click bait out there that, IMO, taking it all with a grain of salt is probably wise.