This is an excerpt from reporter Scott Johnson's blog, which focuses on the effects of violence and trauma on the community. Go to www.oaklandeffect.com for updates on his reporting.

Two mass shooting incidents have occurred in less than a week. The first took place Tuesday in Portland, Ore., when Jacob Tyler Roberts walked into the Clackamas Town Center mall wearing a mask and carrying an AR-15 semi-automatic rifle and opened fire, killing two before his gun jammed. At least 100 police responded to the scene, but it was too late. The two victims were dead. By the time they found Roberts, he had turned his rifle on himself.

The second, much more deadly, shooting occurred early Friday morning on the other side of the country. A man walked into the Sandy Hook Elementary School in Newtown, Conn., and started shooting. At the latest count, 20 children and six adults were killed, and an untold number of students were sent to the hospital with various injuries. The shooter also killed himself.

So more than 600 children¿, from kindergarten through fourth grade, were subjected to a multidimensional horror show on a Friday morning a week¿ before school lets out for the holidays. Many of these children, the most resilient, may move beyond this, recover and heal and go on to have productive and happy lives. But the truth is that many will not, and this one day will leave a lasting imprint of trauma on their brains for years to come.

Twitter lit up with the latest sad, predictable and ultimately very revealing comments about what this latest shooting atrocity means.

"If this isn't a call to beef up mental health services I don't know what is," tweeted Bay Area post-traumatic stress disorder expert Susan Pease Bannit, adding the hashtags #prevention and #insanity to her tweet.

"If you must shoot people how about don't shoot kids," wrote another Tweeter, Spideeboi, "Seems like even crazy people should have a code."

Most of the tweets and comments on news articles reflected something simpler -- sheer bafflement, disgust, sadness, anger, rage.

Stephen Delgiadice, a parent of a young girl who attended the school in Connecticut, told The Associated Press that he had always thought Newtown was "the safest place in America." I wondered, suddenly, what Oakland parents are thinking.

Quite apart from the debate on guns, this latest shooting also got me thinking about the mental health of the shooters. (And also, parenthetically, about how often I seem to be writing about shootings these days.) Roberts, the gunman in Oregon, may have been pushed over the edge by a recent breakup, according to some news reports.

What, one wonders, has happened to all of these gunmen, one after another, who seem like a plague on the nation's peace of mind? This is no excuse for their behavior, but I wonder who we are to hold accountable for their mental health? It seems to me that responding to these shootings only after they have occurred and not before is, in a way, a form of insanity, as Pease Bannit pointed out in her Tweet. To continue to behave in the same way and expect different results is, indeed, a form of madness.

Making it harder for unstable people to access dangerous weapons is surely one way to go about it. That, after all, was the rationale, was it not, for President George W. Bush's invasion of Iraq -- a pre-emptive strike to prevent a dangerous man from using weapons of mass destruction? So what is our pre-emptive strike against unstable people killing innocent children in this country?

There is science to back up the notion that traumatized people move into more trauma as adults. Researchers have known for quite a while now that soldiers who develop PTSD after deployments to Iraq and Afghanistan show far higher rates of childhood trauma than soldiers who do not, regardless of the intensity of their combat experience. In fact, all other things being equal, soldiering can often be a positive, bonding experience that strengthens human ties and connects people to one another, according to research. But if there is a history of childhood trauma, say physical or mental abuse, war and its attendant stresses can be a trigger for major traumatic stress and, as we have seen, violent behavior.

May we soon see our way out of this darkness.

A note regarding last week's column about the effect of stray bullets on a city's peace of mind: My apologies are in order. I seem to have gotten some of my math wrong, as several of you pointed out. Thanks for bringing it to my attention. We do know that people die all the time from stray bullets. Can anyone out there help shed some light on just how many in Oakland? Any help would be most appreciated.

Contact Scott Johnson at 510-208-6429 or scjohnson@bayareanewsgroup.com.