A stabbing in Boston

My son heard some teenagers talking, casually, matter of factly, about this stabbing. I’m reminded of lines from W. H. Auden’s “The Shield of Achilles” (1952):

    That girls are raped, that two boys knife a third,
    Were axioms to him, who’d never heard
Of any world where promises were kept,
Or one could weep because another wept.