4th amendment ????
If the FBI is offering bounties, then - irrespective of whether it's a formal arrangement, or ad-hoc, there is a *very* good argument that Geek Squad/Best Buy are acting as "agents of the state".
The moment that relationship is established to the satisfaction of a court, then the defendant has the immediate (and retrospective) protection from unlawful searches provided by the US Constitutions fourth amendment. Which would require that the FBI had a warrant *before* they went a-snoopin'
Add that to the fruit of the poison tree doctrine, and this is a very shaky case. Generally US law is very clear that you can't break the law to enforce the law. (Unlike the UK where i's positively encouraged)