"All in all it's been a tough week," he said. "But we've seen the character of our country once more."
The marathon blasts and the hunt for the suspects that both terrorized Boston and captivated the country were the predominant worries at the White House. But the capture of one suspect Friday, following the death in a shootout of another, capped a frenzied week in Boston, Washington and elsewhere around the country.
A massive explosion leveled a Texas fertilizer plant Wednesday, leaving at least 14 people dead, 200 injured and a staggering 60 others still unaccounted. On Tuesday, letters addressed to Obama and to a U.S. senator were found to contain traces of poisonous ricin. An Elvis impersonator was arrested and charged with threatening the president's life.
"I'm confident that we have the courage and the resilience and the sprit to overcome these challenges and to go forward," Obama said late Friday at the White House, just over an hour after law-enforcement officials apprehended 19-year-old Dzhokhar Tsarnaev as a suspect in Monday's explosions at Boston's venerable race.
Three people were killed and more than 180 injured in the blasts. A Massachusetts Institute of Technology policeman was killed and another police officer was severely wounded during the manhunt .
Tsarnaev's older brother, 26-year-old Tamerlan Tsarnaev, was also wanted in the bombings and died earlier Friday in an attempt to escape police. The two men were identified by authorities and relatives as ethnic Chechens from southern Russia who had been in the U.S. for about a decade.
Obama called the two men "terrorists" and said Friday's capture "closed an important chapter in this tragedy."
Still he added: "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."
"The families of those killed so senselessly deserve answers, the wounded, some of whom now have to learn to stand, walk and live again deserve answers," he added.
His remarks came a few hours after Obama spoke to Russian President Vladimir Putin to thank him for what the White House described as close cooperation on counter-terrorism, "including in the wake of the Boston attack." Putin expressed condolences for the victims in Boston.
In his comments to reporters late Friday Obama cautioned against a rush to judgment about the motivations of the suspects and "certainly not about entire groups of people."
"That's why we have investigations, that's why we relentlessly gather the facts, that's why we have courts," he said.
The president also acknowledged the fertilizer plant disaster in West Texas, which he described "tightknit community in Texas devastated by a terrible explosion."
"I want them to know that they are not forgotten," he said, pledging to provide resources to recover and rebuild.
The president's praise for law enforcement was echoed by Republican leaders on Capitol Hill. House Speaker John Boehner of Ohio called their actions "a job well done under trying circumstances."
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