BOSTON - Survivors, first-responders and public officials have observed a moment of silence near the Boston Marathon finish line to mark the moment two pressure cooker bombs exploded a year ago.
Three people were killed and 260 others injured in the attacks. MIT police officer Sean Collier was killed several days later, allegedly by the bombing suspects.
This year's running of the Boston Marathon, expected to be the second-largest in history, will take place on Monday.
About 2,500 people attended an invitation-only tribute at the Hynes Convention Center, then walked in the rain to the finish line for the moment of silence. Bells were rung and a flag was raised by Officer Richard Donohue, who was badly injured during a shootout with the bombing suspects.
Obama has silent moment for Boston bombing
President Barack Obama also paid tribute to the victims of the Boston Marathon bombing on its first anniversary with a moment of silence in the Oval Office.
The White House says Obama and his aides held the remembrance privately Tuesday afternoon.
In a written statement, Obama praised the courage and leadership of Bostonians in the wake of tragedy. He said those injured have been awe-inspiring in their recovery.
Obama says this year's race, scheduled for Monday, will, in his words, "show the world the meaning of Boston Strong as a city chooses to run again."
Vice President Joe Biden is in Boston for a memorial service. He says those who lost loved ones are an inspiration for other Americans dealing with tragedy.
Authorities say two brothers planned and orchestrated the attack. Tamerlan Tsarnaev died following a shootout with police. Dzhokhar Tsarnaev is awaiting trial.