TODAY | April 20, 2013
>>> as we mentioned, president obama appeared at the white house briefing room last night. he thanked authorities and said many unanswered questions remain. nbc's kristen welker is there this morning. kristen, good morning to you.
>> all in all this has been a tough week.
>> reporter: in a late-night appearance in the white house briefing room, president obama praised the quick work of the fbi, state and local officials who brought an end to five days of terror.
>> and tonight because of their determined efforts we've closed an important chapter in this tragedy.
>> reporter: administration officials say fbi director robert mueller broke the news to the president that federal agents had arrested the second suspect. homeland security adviser lisa monaco also briefed the president.
>> how did they plan and carry out these attacks and did they receive help?
>> reporter: the comments cap an extraordinary day which saw the boston area go into lockdown mode hours after the president had visited for a thursday interfaith prayer vigil.
>> in this moment of grief we join you in saying, boston, you're my home.
>> reporter: the president received regular updates from top advisers on friday including a morning briefing with his entire national security team in the situation room and one in the afternoon which included calls to boston mayor tom menino . the president stayed out of public view until it was clear boston's unthinkable ordeal was finally over.
>> as president, i'm confident that we have the courage and the resilience and the spirit to overcome these challenges. and to go forward. as one nation under god, indifficult adviindif indivisible with liberty and justice