A couple of observations.
One. The worst job I can think of right now, would be any of the first responders to that school. Walking into a scene with 20 five and six year old children shot to death...I don't know if my own sanity could survive. I wouldn't be surprised to learn that over the next years one or more of the first responding police or EMT people become alcoholics, divorce, or even commit suicide.
Two. Some people (the ones who are not already clamoring for more gun control) are saying we need to do more to find these people before they commit their heinous acts. How? What are really the signs? A friend of mine, a widow, became custodian of her grandson because no one else in the family would take him. He's been arrested a few times, bought a car and then drove it into the backyard and beat it to pieces with a sledge hammer, walked up and down the street with an ax glaring at neighbors. He told my friend that he was probably going to hurt her one day. Still no help from the rest of the family, including the kid's divorced parents. He was taken into a mental facility, then released with medications that he would not take. So bad that my friend, the next time the guy was arrested, sold her house and disappeared for her own protection. The kid is on the loose again. This case seems like a future disaster, but there is no one to do anything about it.
Last night our twin 6 year old granddaughters spent the night. On the way over one started hitting the other, because "She told you the story I wanted to tell, and it was my story!" Early warning, or no-worries sibling rivalry? How does anyone really know before it's too late?
Three. The news reports that the handguns and AR belonged to the killer's mother, who apparently was the his first victim. I guess she had no clue her son was insane, or those guns would have been locked in a safe...like mine are, except for the one I'm wearing which also gets locked in a Gunvault (r) handgun box on the nightstand overnight. There may be more to the mother's story that we've yet to learn.
Finally, an interesting statistic I just heard. More people are murdered with knives in Mexico than all murders with any weapon in the U.S. combined. Strict gun laws just change weapons, not behavior.