U.S. President Barack Obama has pledged to bring to justice the perpetrators of the Boston Marathon bombings -- the worst act of terror to affect civilians in America since the September 11, 2001 attacks.
Obama attended an interfaith service in Boston on April 18 to honor the three people killed and more than 170 injured twin explosions at the finish line of the Boston Marathon on April 15.
In a highly emotional address, Obama insisted that those responsible for the attack cannot hide.
"We will find you, we will hold you accountable, but more than that -- our fidelity to our way of life, to our free and open society will only grow stronger," he said.
The U.S. president evoked the memory of the three people who died in the blasts -- eight-year-old Martin Richard, 29-year-old Krystle Campbel, and Lu Lingzi, a Boston University graduate student from China.
Obama also had words of support for the wounded, some of whom have had limbs amputated as a result of the explosions.
"Our prayers are with the injured," he said. "So many wounded...some gravely. From their beds some are surely watching us gather here today and if you are, know this -- as you begin this long journey of recovery, your city is with you, your commonwealth is with you, your country is with you, we will all be with you as you learn to stand, and walk, and, yes, run again. Of that I have no doubt -- you will run again."
No arrests have been officially announced so far.
Homeland Security Secretary Janet Napolitano said the FBI wants to speak with two men seen in at least one video recording from the marathon, but she added she isn't calling them suspects.
The images have not been publicly released.
Without providing details of the men's appearance or what the video shows, Napolitano told the House of Representatives Homeland Security Committee that "there is some video that raised the question" of two men.
She said the investigation is continuing "apace."
Investigators say the blasts are suspected of being caused by devices made from metal pressure-cookers.
With reporting by AP, Reuters, and CNN