By repercussions do you mean echoes or secondary explosions? It could have been a large caliber firearm; perhaps a .44 magnum or larger. Lack of echoes would indicate it was in an open area not near any buildings for the sound to bounce.
7 nations join U.S. in terror drill to safeguard Panama Canal
http://www.suntimes.com/output/news/cst-nws-panama16.html
D.C. exasperated by security measures
http://www.suntimes.com/output/news/cst-nws-secure16.html
No echo-No secondary anything
Would a large any weapon shake a brick building?
It was a distinct, loud boom unlike anything I've ever heard