However it is a Federal law, which is enforced frequently by this and previous administrations. The FBI and Federal attorney in LA must be asleep. In fairness, an incident like this "making the case" would be a function of the local authorities, the FBI would not have been looking for this in advance. They should be now, particularly in liberal cities where there will be political pressure to look the other way.
Or on the side of the terrorists, they way they were during the BLM/Antifa riots.