This event WAS preventable and it doesn't take 20/20 hindsight to see that. The gunman had been stripped of his right to own guns based on previous weapons and assault charges, had his neighbors complaining of him shooting, and the Sheriff's Dept. failed to do more than knock on his door a couple of times which he didn't answer.
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"However vast the darkness, we must provide our own light."
Stanley Kubrick
"Tomorrow belongs to those who can hear it coming."
David Bowie