But he emphasized that the alleged terrorists have "already failed" if they sought to divide America.
"Tonight, our nation is in debt to the people of Boston and the people of Massachusetts," Obama said in hastily arranged public remarks in the White House briefing room. "After a vicious attack on their city, Bostonians responded with resolve and determination. They did their part as citizens and partners in this investigation.
"Obviously, tonight, there are still many unanswered questions. Among them: Why did young men who grew up and studied here as part of our communities and our country resort to such violence? How did they plan and carry out these attacks? And did they receive any help?" he said, in the clearest-yet suggestion that violence might have had roots overseas. The families of those killed and those who were wounded "deserve answers," he said, and federal law-enforcement agencies will deploy "all the necessary resources" to give them that satisfaction.
We will determine what happened. We will investigate any associations that these terrorists may have had. And we’ll continue to do whatever we have to do to keep our people safe," Obama said.