By Scott Malone

BOSTON (Reuters) - Boston marked the second anniversary of the deadly attack on its annual marathon on Wednesday with a quiet ceremony at the site where three died, unveiling a pair of banners marked with a heart.

Mayor Marty Walsh joined a group of survivors of the April 15, 2013, blasts, including Jane and Henry Richard, whose 8-year-old brother Martin was the youngest killed, as well as Jeff Bauman, who lost both legs. Some 264 people, including spectators, volunteers at runners at the Boston Marathon were injured.

At 2:49 p.m. ET (1849 GMT) New England's largest city will observe a moment of silence to mark the time the first bomb went off.

"Our thoughts and prayers are with the victims and their families, who seek to make sense of that awful day," said Massachusetts Governor Charlie Baker. "Those most affected by the events of two years ago have shown us all the way back with their courage, grace and determination.

The anniversary comes amid a break in the trial of Dzhokhar Tsarnaev, who was convicted last week of carrying out the bombing attack, before the same jury that found him guilty decides whether to sentence him to death or life in prison.

Tsarnaev, 21, was the younger of two brothers who carried out the attack and three days later shot dead a police officer as they prepared to flee the city. His older brother, 26-year-old Tamerlan, died following a gunfight with police after that shooting.

Three people died in the bombing attack: 8-year-old Martin Richard; Chinese exchange student Lingzi Lu, 23; and restaurant manager Krystle Campbell, 29. Massachusetts Institute of Technology police officer Sean Collier, 26, was shot dead three days later.

Collier's sister this week said on social media she did not believe Tsarnaev, an ethnic Chechen who left a note suggesting the attack was an act of retribution for U.S. military campaigns in Muslim-dominated countries, deserved to die.

"Whenever someone speaks out against the death penalty, they are challenged to imagine how they would feel if someone they love were killed. I’ve been given that horrible perspective," Collier's sister, Jennifer Lemmerman, wrote on Facebook.

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Other voices have been less forgiving, among them local CBS commentator Jon Keller, who had first argued against pursuing the death penalty.

"I changed my mind, and in the wake of the verdict I'm not hearing anything to change it again," Keller wrote earlier this month.

(Editing by Eric Walsh and Lisa Lambert)