A horrible atrocity.
The perpetrator deserves the most severe penalty possible. But, in a way, the fact this is the deadliest anti-Semitic attack in American history actually speaks well for the US. It would be nowhere near the deadliest in most European and Middle Eastern nations - and not just those touched by the Holocaust. America is far from free of anti-Semitism, either historically or today. But we have less of it than almost any other nation with a significant Jewish population.