But he didn’t intend to commit the crime, which is the element of mens rea.
The records show that he took every step to avoid committing a crime. That is enough to dismiss criminal intent.
I understand what you are saying.
But the defendant didn't do EVERYTHING he could do in order not to be breaking the law. He didn't study the laws of DC and he didn't avoid having the illegal magazines.
I'm not a lawyer and I am trying to understand under what circumstances a defendent is "not guilty" simply because he didn't know the law. In the last few days I have seen postings of the DC law and I don't recall seeing any mention of "intent".
Several years ago I travelled with firearms on a trip through the U.S., visiting about half of the states. Despite my best efforts I probably missed a few laws that could have gotten me in trouble. Would I have been "not guilty" because I didn't know, or just "not punished"?