In the aftermath of deadly explosions at the Boston Marathon, two main questions --- who and why?<br/> <br />At the White House, President Barack Obama addressed the blast.<br/> <br />SOUNDBITE: U.S. President Barack Obama saying: "We don't yet have all the answers but we do know that multiple people have been wounded, some gravely, in explosions at the Boston Marathon."<br/> <br />In fact two people have been reportedly killed in the blasts... with dozens injured.<br/> <br />Police were put on alert in major cities across the U.S, including this beefed up security in New York's Times Square.<br/> <br />Obama vowed those responsible we be held accountable.<br/> <br />SOUNDBITE: U.S. President Barack Obama saying: "But, make no mistake, we will get to the bottom of this, and we will find out who did this, we will find out why they did this."<br/> <br />"Any responsible individuals, any responsible groups, will feel the full weight of justice."<br/> <br />After Obama's statement, the White House called the explosions an act of
