The Lansing State Journal has details. (The decision not to charge the man happened in September, but I just heard about it now, and the newspaper apparently has extra details that weren’t available then.) The bottom line as to the charges:
The man didn’t damage anyone else’s property. The Quran he burned was his own. He didn’t make physical contact with another person. So proving he had threatened to do one of those things, and that there was a reasonable expectation that he would, would have been the only way to charge him under Michigan’s ethnic intimidation law.
I’m inclined to think that this is right. Burning a Koran as such is not a crime. Burning it in a context where it would reasonably be seen as a deliberate and particularized threat of future crime against some particular victim might well be a crime, and would fit within the First Amendment exception for threats. But I suspect that in context seeing a burned Koran on the doorstep of a mosque would be seen as an expression of hostility and hatred, but not a specific threat. In any case, the story struck me as worth noting.
The story also notes, “There was one other crime the man might have been charged with: littering. East Lansing officials decided not to try, because it ‘would have trivialized the offense,’ said assistant city attorney Tom Yeadon.” My sense is that there would also have been a possible First Amendment problem if the littering prosecution was motivated by the message. I doubt that, say, the prosecutor would prosecute someone for littering if he left hostile anti-NRA messages on the doorstep of the NRA office, or hostile anti-American messages on the doorstep of an American Legion office. If so, then the prosecutor can’t selectively prosecute those who supposedly litter (if this is indeed littering) using anti-Islam messages.