Anyone who has been to Boston on July 4th knows how crowded it gets with people coming to hear the Boston Pops and watch the fireworks, if they bombed that event the carnage would have been catastrophic.

Via CNN:

The bombs used in the Boston Marathon attack were built in the apartment that suspect Tamerlan Tsarnaev shared with his wife and child, a U.S. law enforcement official with first-hand knowledge of the investigation told CNN on Thursday. The official was not authorized to release the information.

Tamerlan and Dzhokhar Tsarnaev initially planned to carry out an attack on July 4, but their bombs were ready earlier than they expected and they decided to move up the date, a U.S. law enforcement official told CNN on Thursday.