Just out of curiosity, is it actually legal for the FBI to send someone a package, then use that package as pretense to arrest them? I thought there were all sorts of rules against that.
One way to look at it is that law enforcement people are trained in what evidence is admissible and what isn't, so they understand and have an incentive to follow proper procedures. But this can become self-fulfilling if people give law enforcement unlimited benefit of the doubt, allowing abuses to happen unchecked.
If you're referring to the arrest of Green in the beginning, the authorities had built up a case that Green was a major player in the Silk Road and the package delivery was the final confirmation.
You seem to be talking about entrapment, but entrapment is when law enforcement induces someone to commit a crime they would otherwise not have committed. Here they had evidence that Green routinely arranged and received drug shipments, and that this final shipment made by an undercover officer was part of that routine.
