In Boston Marathon explosions, Obama vows 'we will find out' who's responsible

President Barack Obama, addressing the nation about the Boston Marathon explosions, pledged "we will find out who did this, and we will hold them accountable."

Obama said urged Americans to "say a prayer for Boston" while the federal government responds and provides full resources to the investigation.

"We still do not know who did this or why, and people should not jump to conclusions . . . but make no mistake, we will get to the bottom of this," Obama said. "Any responsible individual, any responsible groups, will feel the full weight of justice."

Obama noted that the explosions near the end of the marathon left multiple people wounded, "some gravely."

The president noted that it is Patriots' Day in Boston, "a day that draws the world to Boston's streets."

Obama said Boston is a "tough and resilient town, and so are its people."

"All Americans stand with the people of Boston," he said.