President Obama just addressed the nation from the White House press room:
The nation will remember Boston in their prayers tonight. Federal officials are mobilizing resources to help. I've notified leaders of both parties; they agree that on days like this, there are no political parties.
Police, firefighters, first responders, and the National Guard responded heroically. We salute all those who responded so quickly and professionally to this tragedy.
We still do not know who did this or why; we still don't have all the facts. We will get to the bottom of this. We will find who did this and we will find out why they did this. Any responsible people or groups will feel the full weight of justice.
Today is Patriots Day, a day that reflects the freedom Boston has celebrated throughout its history. Boston is a tough and resilient town; so are its people. I'm sure the people of Boston will pull together.
As we get more information, our teams will provide more briefings. We'll find out who did this, and we'll hold them accountable.