The evidence would come up in court. If the cop isn't recording it to say "look there, he knew!" then it would be on the cop to prove him wrong when he says "Nobody said shit about a crime..."
What's being left out is the fact the the under cover officer made it clear that he was exchanging Bitcoins to engage in a criminal activity.
~BCX~
Yeah, because the police would never make false statements, plant evidence, invent probable cause, or lie to the media in pursuit of a headline-grabbing sting operation with no element of public service to it.
Yes. I don't understand how Bitcoin can ever be secure if the incentives to centralized mining pools are strong enough to grow a single pool operator to a known 42% of the network hashower. If I were running Ghash.IO, I'd be hiding some of that quietly, over time, so I can own 51% or more and control the network without anyone realizing it.