Mass murderers in the U.S. are typically the mentally ill.  There are many markers:  isolated, anti-social, history of mental illness, &quot;neighbors considered him a little strange&quot;, family who are fully aware (&quot;we always feared this would happen&quot; or &quot;he scared us&quot;).<p>Of course, you can&#x27;t just go pick up every strange person and lock them away, or 20% of us might be incarcerated.  But we can definitely have better scrutiny of sociopathic children in junior high and high school, and steer them into treatment that might help protect them from hurting themselves and others.  We&#x27;ve gone from excessive incarceration back in the 1950s to inadequate attention to the mentally ill since the 1970s, when the flawed policy of mainstreaming became popular.<p>The Columbine massacre was perpetrated by two disturbed boys whose families suspected something.  Afterwards one of their dads said &quot;That sounds like him.&quot;  Well, if you suspected violence, why didn&#x27;t you do something about it sooner?<p>The other kind of mass murderers today are ideology-driven Muslims.  3,000 on 9&#x2F;11.  Dozens at a Texas base.  14 in San Bernardino.  I suspect there will be many more coming.  These people are quite possibly mentally ill, sociopathic, something wrong upstairs.  The ideology gives them a focus for their delusions.  We don&#x27;t need to go after Muslims in general; we need to focus on the unstable ones who are headed for trouble.<p>It&#x27;s going to take clear heads and a lot of work, and in my opinion the very worst approach is to sweep all these problems under the carpet and simply tap everyone&#x27;s phone and email.  That&#x27;s just an evasion and confers a dangerous sense of complacence.