Kent State student John Filo's Pulitzer Prize-winning photo of Mary Ann Vecchio discovering the slain Jeffrey Miller. 39 years ago today, Ohio National Guardsmen opened fire on an unarmed group of antiwar demonstrators for 13 seconds, killing four students. My piece last year, is the definitive history. (And it brought out a pesky right wing troll, as well as my very first IP banning of this site.)
I don't have anything to add to what I wrote last year.
Also see: Mike and Kendra's May 4th website for documentation, photos, follow-ups, and everything else you ever wanted to know.
And rest in peace, dear ones: Allison Krause, Jeffrey Miller, Sandra Scheuer and William Knox Schroeder.