This editorial suggests one theory of why officials announced the investigation now, but refused to say which group submitted the faulty registrations.

But I wonder if that information is being kept under wraps because it was Republican-affiliated groups that engaged in submitting the fraudulent documents. I’ve seen rumors to that effect online but I don’t know whether that is true or not. But keeping this information private until after the election could serve partisan purposes.

Or maybe there is a more benign explanation, such as not prejudicing an ongoing investigation.

But announcing the issue without naming who did it (while knowing who did it) or charging any individuals with crimes seems odd.

UPDATE: I missed this Adam Bonin tweet earlier.

SECOND UPDATE: We now have good evidence that it is not Republican-affiliated groups involved, . Details at Votebeat.