This sounds stupid, but this strategy would probably work if he was dumb enough to talk to police.
Detective (preferably black or hispanic) "we found a video that you were in throwing a bicycle lock at victim (truth).
Professor, "that wasn't me, it was somebody who looked similar" (lie)
Detective, "you know I hate these nazi-lovers as much as you do (lie), it was a nice shot (truth)--I wish I could have seen it in person (truth)--- fake sob story of a grandparent at the hands of white people (lie). You're a professor, you're much too smart (lie) to be messing around with these idiots (lie). We have a surveillance video from the building down the street with conclusive evidence it was you walking to the spot of the incident (lie).
Then give whatever other evidence they have, maybe the bike lock order receipt. Tell him another person they identified ratted him out or whatever. It would take a microsecond for a girlfriend to turn on him.