(Updates with quotes from beginning of memorial ceremony, other details)
By Scott Malone
BOSTON, April 15 (Reuters) - Boston marked the anniversary of the Boston Marathon bombing, which killed three people and injured 264, on Tuesday with a memorial service to feature remarks by survivors of the attack and U.S. Vice President Joe Biden.
About 2,500 invited guests attended the memorial at Boston's Hynes Convention Center, just blocks from the race's finish line, where a pair of homemade pressure-cooker bombs detonated a year ago, ripping through the crowd of thousands of spectators.
"You have struggled to get through the good days and the bad," said former Mayor Thomas Menino, who stepped down at the end of last year after his sixth term in office. "I know because so many of you have told me about this year of firsts. First birthday without your beloved son, first holiday without your daughter, first July 4 where the fireworks scared you."
Menino, who had been hospitalized at the time of the blasts but responded to the scene against his doctor's orders, praised Boston residents' response to the bombing.
"You are strong at this broken place," said Menino. "That strength thrives even in the heartaches of today because of the compassion that took over this city."
The April 15, 2013, attacks, which federal prosecutors have blamed on a pair of ethnic Chechen brothers, killed Martin Richard, 8, Krystle Campbell, 29, and Chinese national Lu Lingzi, 23. It was the worst mass-casualty attack on U.S. soil since the Sept. 11, 2011 attacks that killed some 3,000 people.
Three days after the bombings, a Massachusetts Institute of Technology police officer, Sean Collier, 27, was shot dead by the same brothers, prosecutors said.
As Tuesday's formal ceremony began, Roxbury Presbyterian Church Rev. Liz Walker summoned the memory of all four of the slain.
"Today we remember Krystle Campbell, her energy and zest, her adventure and passion, a generosity of spirit, a light that will never fade," Walker said. "We remember Lingzi Lu, heart and sparking eyes, music and guilelessness, a welcome smile that beans forever. ... We remember Martin Richard, tough and competitive, kind and caring, a Dorchester kid through and through. And we will remember Sean Collier, dedicated, with honor, trusted and respected."
Before the ceremony, Mayor Martin Walsh and Roman Catholic Cardinal Sean O'Malley, accompanied by the families of the three killed in the bombing, began the day on a quiet note, visiting wreathes lain at the spots on Boylston Street where the bombs went off.
They embraced and spoke softly as bagpipes played.
President Barack Obama praised the city's response to the attack.
"Today, we recognize the incredible courage and leadership of so many Bostonians in the wake of unspeakable tragedy," Obama said in a statement. "One year later, we also stand in awe of the men and women who continue to inspire us - learning to stand, walk, dance and run again."
After the memorial, which also will feature performances by the Boston Pops and a children's chorus, Boston will observe a moment of silence at 2:49 p.m. EDT (1849 GMT), the time the first bomb went off.
This year's Boston Marathon, set for April 21, will take place under heightened security, with the 36,000 runners and tens of thousands of expected spectators facing new restrictions, including bans on carrying backpacks into the race corridor.
Authorities say the ethnic Chechen brothers, Dzhokhar and Tamerlan Tsarnaev, carried their bombs to the finish line in backpacks.
Three days after the attack, the FBI released pictures of the suspected bombers and asked for the public's help in finding them. That prompted the Tsarnaev brothers to attempt a hasty flight from Boston, which began with them shooting Collier, prosecutors said, in an unsuccessful attempt to steal his gun.
The resulting police chase ended in a gunbattle in the Boston suburb of Watertown. Tamerlan, 26, was killed; Dzhokhar, now 20, escaped before being captured on April 19.
The surviving brother is awaiting trial on charges that carry the possibility of execution if he is convicted. (Editing by Grant McCool, James Dalgleish and Jonathan Oatis)
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