I have read the same thing. I have also read that the State was sued and sued and sued until they finally paid up to the 'survivors' and the gov declared never again would the NG be deployed with ammo.Ref Kent State.
Either Chanel 8 or 19 got a tape and has forensic analysis done and found a shot fired seconds before the Guard fired.
I'll have to hunt for the story. There was a problematic informant (drug) who was likely the shooter.