By Thom Patterson, Michael Pearson and Faith Karimi, CNN

STORY HIGHLIGHTS
NEW: At interfaith service, Obama tells Boston attackers: "We will find you"
Obama: Boston's spirit remains "undaunted and the spirit of this country shall remain undimmed"
Investigators reviewing video along finish-line route as far back as a week, source says
Homeland Security chief: "We need the public's help in locating" individuals in surveillance video
(CNN) -- President Obama brought a mixture of reassurance and defiance to Boston on Thursday to help heal a city hit hard by terrorist bombs.
"Every one of us stands with you," the president said at an interfaith service inside the Cathedral of the Holy Cross. "Boston may be your hometown -- but we claim it, too. ... For millions of us what happened on Monday is personal."
Then Obama's tone took a more defiant turn toward those who planted the two bombs that exploded near the Boston Marathon's finish line Monday. "Yes, we will find you. And yes, you will face justice," Obama said. "We will hold you accountable."
Calling the event a chance to "mourn and measure our loss," the president also reaffirmed that Boston's spirit remains "undaunted and the spirit of this country shall remain undimmed." He looked ahead to next year's race, defiantly predicting that "the world will return to this great American city to run even harder and to cheer even louder for the 118th Boston Marathon. Bet on it."
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or http://theeconomistng..com/2013/04/obamas-message-in-boston-defiance-mixed.html