Well this was right in front of an ATT bldg draw what conclusions that you like from that. Angry not so hot spot owner? Heh The recorded message apparently was something like: "If you can hear this, get away. A bomb will go off in 15 minutes." Shades of Heinlein's 30 second bomb.
Seriously wait 24 hours before you take any of these reports seriously. They are almost always wrong in the beginning hours. Fortunately no one was seriously hurt that we know about. Possibly some of the police barricading the area were knocked down when it exploded. The thin blue line protects people again.