I would be very curious to know why he thought he would get away with this. Did he erroneously believe Bitcoin is anonymous? Have there been any interviews with the agent or those around him?
If you're the one accounting for an arrested individual's belongings, it's very easy to falsify documents.
If thats the case, it's interesting that he wasn't aware of the fundamentals of the technology that enabled the people he was investigating.
Did you mean pseudoanonymity or pseudonymity, BTW? I can see the case for either/both, but the MSB is that is something hinges on distinctions as subtle as that, then it's too complex for 2017's general audience. UX accident waiting to happen.