A US Justice Department report faulted local authorities Wednesday for failing to update a federal database used in background checks for gun sales, sometimes with "tragic consequences." The inspector general's report cited the June 2015 mass slaying at a black church in Charleston, South Carolina as one such case. Dylan Roof, a white supremacist who shot and killed nine churchgoers in cold blood, should not have been authorized to buy guns since he had been arrested previously for a drug offense.Roof had not been convicted of a crime (drug habituation) at the time, so he was not YET identified as a person who should not be allowed to own a firearm. Also, the background-check was (reportedly) delayed .. perhaps for that reason ... for more than the statuary limit of time.
The local authorities could not identify Roof as a felon because of the lack of conviction. He was, in fact, only accused of a crime. At the point where he received a firearm, he was not legally constrained from firearms ownership. "Local Authorities" could not identify him as a person who was a danger to his community, lacking a conviction. This might explain, at least in part, the delay which resulted in his not being identified as a "person" who should not possess a firearm.
Calls for an 'Australian Style" Gun Control Process would probably not have affected his possession.