The nation has "closed an important chapter" in its response to a terrorist attack on Monday, President Barack Obama said Friday evening at the White House, capping what the president called a "tough week" that captured much of the nation's attention.

After a day of anxious waiting that played out live on national television and in social media, police apprehended Dzhokhar Tsarnaev — the second, remaining suspect in Monday's bombing of the Boston Marathon — alive following a daylong manhunt that shut down much of the Boston metro area. 

"Boston police and state police and local police across the commonwealth of Massachusetts responded with professionalism and bravery over five long days," the president said at the White House. "And tonight because of their determined efforts, we've closed an important chapter in this tragedy."

The lockdown followed an early morning shootout between Dzhokhar Tsarnaev and his older brother, Tamerlan Tsarnaev, and police that left the elder brother dead. Police spent most of the day going door-to-door in the Boston suburb of Watertown in search of the younger brother.

But the president suggested there was much work ahead as investigators begin to delve more into the planning and execution of Monday's attack, and that he'd asked the FBI, Department of Homeland Security and intelligence agencies to continue to deploy resources for its 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?" Obama said. "The families of those killed so senselessly deserve answers."

The president added: "We will determine what happened, we will investigate any associations that these terrorists may have had, and we'll continue to do what we have to do to keep our people safe."

Obama was also pointed in saying the alleged bombers had "failed" in propagating any ideology underpinning their attack on the marathon, which left three dead and dozens others injured.

Obama was told of the news by Robert Mueller, the head of the FBI, which has been leading the federal investigation into the bombing.

White House officials said that Obama had been kept apprised of the developments on the manhunt throughout the day in briefings with his national security team. The most recent briefing disclosed to the press concluded shortly after 4 p.m. ET, a White House official said, in the Oval Office. During that meeting, the president called both Massachusetts Gov. Deval Patrick, D, and Mayor Thomas Menino, D, for regular updates about the investigation. 

The president also spoke Friday with Russian President Vladimir Putin, whose nation has been plagued by clashes with Chechnya. Obama "praised the close cooperation that the United States has received from Russia on counter-terrorism, including in the wake of the Boston attack," according to an official White House account of the call.

But as investigators pored into the backgrounds of the Tsarnaev brothers, the president warned against any rush to judgment.

"When a tragedy like this happens … it's important that we do this right. That's why we have investigations. That's why we relentlessly gather the facts. That's why we have courts," he said. "That's why we take care not to rush to judgment -- not about motivations of individuals, certainly not about entire groups of people."

There was a small element of politics amid an essentially criminal pursuit of the at-large suspect in the Marathon bombings, an event that was regarded as a terrorist attack. Sen. Lindsey Graham, S.C., and Rep. Peter King, N.Y., both Republicans who speak out frequently on national security issues, quickly urged law enforcement against reading Tsarnaev his Miranda rights, which would entitle him to certain legal rights in the criminal justice system. 

But the administration said it would invoke a public safety exception to the Miranda rule shortly after Tsarnaev's apprehension, and would withhold the warning normally read to suspects under arrest when the accused terrorist is physically able to be interrogated.

Obama also used the national speaking slot to pledge assistance to the victims of an explosion this week at a fertilizer plant in West, Texas.

"I want them to know that they are not forgotten," he said. "Our thoughts, our prayers are with the people of West, Texas, where so many good people lost their lives, some lost their homes, many are injured, many are still missing."

And as if to cap the week's flurry of activity, Obama termed this one a "tough week," but said he was confident the U.S. had the resilience to overcome its challenges.

This story was originally published on Fri Apr 19, 2013 11:38 PM EDT

Jason Reed / Reuters

Senator Chuck Schumer, part of the U.S. Senate's "Gang on Eight", speaks during a news briefing on Capitol Hill, April 18, 2013.

The Boston Marathon bombing and subsequent manhunt for suspects has already become part of the debate over immigration reform in Washington, with one high ranking Republican questioning the screening process that allows immigrants into the United States.

The Senate Judiciary Committee was scheduled to hear testimony from Secretary of Homeland Security Janet Napolitano on the bipartisan immigration overhaul introduced by a group of eight senators, but she had to postpone due to ongoing developments in the search.

A ranking member on the Senate Judiciary Committee, Sen. Charles Grassley, R-Iowa, said at the outset of the committee’s hearing, “Given the events of this week, it’s important for us to understand the gaps and loopholes in our immigration system. While we don’t yet know the immigration status of the people who have terrorized the communities in Massachusetts, when we find out it will help shed light on the weaknesses of our system.” 

Grassley asked, “How can individuals evade authorities and plan such attacks on our soil? How can we beef up security checks on people who wish to enter the United States? How do we ensure that people who wish to do us harm are not eligible for benefits under the immigration laws, including this new bill before us?”

But a few minutes later, Sen. Charles Schumer, D- N.Y. the chief sponsor of the bipartisan immigration overhaul, in an apparent response to Grassley, said one shouldn’t jump to conclusions about the events in Boston “or try to conflate those events with this legislation. In general, we’re a safer country when law enforcement knows who is here – has their fingerprints, photos, et cetera – has conducted background checks and no longer needs to look at needles in haystacks. In addition, both the refugee program and the asylum program have been significantly strengthened in the past five years such that we are much more careful about screening people and determining who should and should not be coming into the country. If there are any changes our homeland security experts tell us need to be made (in his bill), I’m committed to making them….”

In a statement Friday, Frank Sharry, head of America’s Voice Education Fund and a veteran campaigner for an immigration overhaul which would allow a path to legal residence for some of those in the country illegally, said, "It’s premature to jump to final conclusions about the attackers. And it’s shameful that some on the far right are politicizing and demagoguing this issue.” Sharry said some -- whom he did not identify -- are "exploiting this tragedy in hopes of derailing immigration reform."

The Senate will likely debate the bipartisan “Gang of Eight” immigration overhaul next month, but Grassley stressed that the bill ought to be fully debated in committee and open to amendments on the Senate floor.

Referring to the 1986 Simpson-Mazzoli immigration overhaul which was supposed to end illegal immigration and prevent any future amnesty, Grassley said, “We screwed up – and we can’t afford to screw up again.”

The committee was hearing Friday from two witnesses, conservative attorney Peter Kirsanow – who indicated his opposition to the bipartisan bill because he said it would lower wages for U.S. low-skill workers -- and former director of Congressional Budget Office Douglas Holtz-Eakin, who supported the bill.

Related links:

Suspects to carjack victim: We are the bombers 

Who are the brothers accused of the Boston Marathon bombing? 

An empty metropolis: Photos show deserted streets of Boston  

What we know: Timeline of terror hunt

‘Dedicated officer’ gunned down by Boston Marathon suspects at MIT

Slideshow: Bombings at Boston Marathon

Boston bombing spurs Senate debate on tighter immigration screening 

Photos from Bostonians locked down amid terror hunt 

Tweeting police chatter creates confusion over Boston suspect

This story was originally published on Fri Apr 19, 2013 11:47 AM EDT