Resources?
It will take 20x the resources for the FBI to locate Laundrie than the
cost of the Surveillance by the local Police.
I suspect that a small-jurisdiction police chief is probably rather averse to horning-in on an FBI case when he hasn’t been invited; especially when he has his own issues to deal with. (The Freepers may be fixated on this case, but it’s one of thousands that police departments are dealing with all over the country.)
And I’m sure the Chief appreciated a call from someone who doesn’t even live in his state, telling him how to do his job - someone who only knows what he reads on the internet or sees on TV.
(Do you believe that the FBI was not in contact with the NP police early in the game? I don’t think things work that way.)