This appears to have been done with a DEW. The amount of debris that remains is not nearly enough to account for the mass of the building that is missing. There is a massive cloud of dust surrounding the area more than 10 hours later and there are very hot fires the firemen cannot seem to extinguish. The ONLY event we have seen in the US like this was 9-11-2001
They could have done this to take out one high value target individual or a team, they don't care about collateral damage and loss of innocent life.