12 moments in national security for President Obama's team

Two explosions near the finish line of the Boston Marathon on April 15, 2013, killed three and injured more than 260 others. Tamerlan Suspect Tsarnaev died after a violent confrontation with police while his brother, Dzhokhar, was captured. Federal officials have declared the attacks an act of terror. As President Obama announces a new national security team, here is a look at key moments in national security since 2009:

Two explosions near the finish line of the Boston Marathon on April 15, 2013, killed three and injured more than 260 others. Tamerlan Suspect Tsarnaev died after a violent confrontation with police while his brother, Dzhokhar, was captured. Federal officials have declared the attacks an act of terror. As President Obama announces a new national security team, here is a look at key moments in national security since 2009: