I'm sure everyone's heard about the bombing by now so I won't bother linking an article.
My take...
As soon as I saw the aftermath I could tell it wasn't a high order explosion so nothing like TATP or PETN was used, which are typical terrorist favorites. But, even though it was low order, it wasn't enough of something like ANFO to do OKC level damage. I'm guessing something like propane and/or gasoline and/or limited quantities of ANFO and/or some Tannerite. Not a sign of someone that really knew what they were doing.
Looks likely the target was the AT&T hub, however, another sign this person didn't know what they were doing is they failed to take into account these old AT&T hub buildings, especially the ones in metro areas, were built during the Cold War to ensure national phone line redundancy and as such are built with very substantial blast/overpressure resistance. That said, it does look like they did managed to at least disrupt operations.
The recorded evac warning is a bit unusual but between that and it being on Christmas morning at a time likely to be low population in an area known to usually be busy, it looks like the perp deliberately took effort to minimize human casualties so it had to be a directed infrastructure attack. Why a directed infrastructure attack at AT&T? Well...
