Well well well, Zetekitoxin.
>>What are the legal implications of him posessing the animal and how (and to whom) can he legally get rid of it?
The implications of him keeping it, specifically keeping it without authorization, are probably severe. My opinion would be he should contact an attorney--maybe that guy that advertises in Reptiles Magazine wanting herp-related cases, and examine his options. I would think he could make a case if he makes a "good faith" effort to notify authorities that he received the boa through what most likely is a case of mistaken identity, and since it would be impractical and maybe even detrimental (to the individual snake and to the wild population) to return a now-captive boa back to its original habitat, he may either receive special authorization to keep it (as long as he doesn't try to sell it) or at least get it to a zoo without any penalties on his part.
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Chris McMartin
www.mcmartinville.com
I'm Not a Herpetologist, but I Play One on the Internet