Your friend doesn't need a researcher, he needs a vet

>to take or look for since the trail is hot??

300+ hives?
If its ccd 
you really shoud see some dead emergants(20+?)
in at least 10? of the hives (5%?)
And some rear leg symptoms , see below

How much dead brood?
Lots or < 1 frame total?
Examine dead brood. 
Are the majority 20d +-1d?
and rest sealing (8d) +-1d?
At 7d they dry to a white chip,
at 9d looks quite like AFB (after a bit), 
but no smell and skin is intact (and no pin holes or sunken cappings and no unsealed)
(if you are careful uncapping you see intact larvae)

>and any suggestions on what to do with the empty hives?
I recommend burning frames with dead brood,
(or pressure spray brood out, then bleach)

FA (formic) is both a treatment and fumigant
(use it on empties too, wrap stack in plastic)
After formic treatment on empties watch out for wax moth

A full FA treatment twice a year or more often on survivors
I use 250 ml in fiber board in zip-lock perforated bag, 3 weeks
(Ontario method)

>Neighboring hives strong and healthy
Watch near hives closely, watch for unusual rear leg movements
If you don't understand then shake 2 or 3 frames onto a ramp
as if you were hiving a swarm (into their own hive), observe laggards

Feel free to share your observations

dave

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