There is no doubt that the attack on the Boston Marathon, its runners, its fans, and its host city was a terror attack. By its nature – explosive devices specifically designed to maim and kill, placed in a crowd at a celebratory public event – it was clearly intended not only to inflict mass casualties, but also to instill fear in the minds of bystanders, witnesses, and the wider public. Currently available evidence suggests that the perpetrators were the two individuals now identified as Dzhokhar and Tamerlan Tsarnaev. What remains unclear (at this writing) is whether they acted by themselves, or whether there were others involved, or whether there was any organized group involved. That does, of course, matter greatly – and we will find out a good deal more in the days ahead about how and by whom this devastating attack was planned, organized, supported, and executed. But there are already a number of observations that can be made with reasonable assurance about this event that do not depend greatly on knowing more about its genesis. This essay outlines a few of the observations and conclusions that it already seems fair to reach.