The twin bombings at the Boston Marathon drew immediate parallels to the attack on the World Trade Center in New York City a dozen years earlier.
President Obama said those people responsible for the explosions in Boston "will feel the full weight of justice."
At least two people were killed and dozens more injured in bombings during Monday's Boston Marathon.
Federal prosecutors say they will seek the death penalty against Dzhokhar Tsarnaev in the Boston Marathon bombing.
George Zimmerman's acquittal and more events. (1/2/2014)
A look back on 2013 in political pictures.