BOSTON (AP) — The anniversary of the Boston Marathon bombings started with a solemn wreath-laying ceremony Tuesday morning at the site of the twin explosions, the first tribute in a day dedicated to honoring the three people who died, the more than 260 people who were injured, and the first responders, doctors and nurses who helped them.

The ceremony was attended by the families of the three bombing victims — Martin Richard, Krystle Campbell and Lu Lingzi — as well as relatives of Massachusetts Institute of Technology police Officer Sean Collier, who was killed in the aftermath of the blasts.

Gov. Deval Patrick, Mayor Martin Walsh and Boston Cardinal Sean O'Malley were among those who attended the ceremony held in a light rain amid the music of bagpipes. O'Malley offered a prayer.

Vice President Joe Biden, Patrick and former Mayor Tom Menino will be among the dignitaries expected to honor the victims later Tuesday during a program at the Hynes Convention Center. Speakers also will include survivors of the bombing.

Between 2:30 p.m. and 3 p.m., a flag-raising ceremony and moment of silence will be held at the marathon finish line, to mark the time and place where two bombs exploded on April 15, 2013.

Authorities say two brothers planned and orchestrated the attack and later shot and killed Collier during an attempt to steal his gun. Tamerlan Tsarnaev, 26, died following a shootout with police several days after the bombings. Dzhokhar Tsarnaev, 20, has pleaded not guilty to 30 federal charges and is awaiting trial. He faces the possibility of the death penalty.

The Tsarnaevs, ethnic Chechens who lived in the former Soviet republic of Kyrgyzstan and the Dagestan region of Russia, settled in Cambridge, outside Boston, more than a decade ago after moving to the U.S. as children with their family.

Prosecutors have said Dzhokhar Tsarnaev left a hand-scrawled confession condemning U.S. actions in Muslim countries on the inside wall of a boat he was found hiding in following the police shootout.