I know that no words can possibly be the right ones.
Not one person in the "Civilized" world can possibly comprehend the absolute horror of this utterly disgusting and yes, cowardly act.
I have many relatives in the USA, my auntie is living in manhattan, and my mother has been crying all day, she is not able to find out a thing yet, and I can only imagine what the people who are directly local to the area are going through.
Lets hope this does not escalate to something as awfull as full scale war, however, this CANNOT go unpunished without SERIOUS retribution.