The first anniversary of the Boston Marathon bombings started with a wreath-laying ceremony at the site of the twin explosions.

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 when the suspects, now on the run, stole his gun.

The family of Martin Richard, an eight-year-old boy killed in the blast, attend a wreath-laying ceremony on the first anniversary of the 2013 Boston Marathon Bombing
The family of Martin Richard, an eight-year-old boy killed in the blast, attend a wreath-laying ceremony on the first anniversary of the 2013 Boston Marathon BombingGetty
The family of Lu Lingzi, a 23-year-old Boston University graduate student from Shenyang in China, pay their respects
The family of Lu Lingzi, a 23-year-old Boston University graduate student from Shenyang in China, pay their respectsGetty
Police and fire department members guard the site of one of the bombs following a wreath-laying ceremony
Police and fire department members guard the site of one of the bombs following a wreath-laying ceremonyGetty
Members of the Boston Police Department, Boston Fire Department and Massachusetts State Police rehearse for the wreath-laying
Members of the Boston Police Department, Boston Fire Department and Massachusetts State Police rehearse for the wreath-layingGetty
Flowers on the finish line
Flowers on the finish lineGetty
Crosses bearing the names of the people killed are displayed in an exhibit at the Boston Public Library to commemorate the 2013 Boston Marathon bombings
Crosses bearing the names of the people killed are displayed in an exhibit at the Boston Public Library to commemorate the 2013 Boston Marathon bombingsGetty
Runners' shoes and other objects that were left at makeshift memorials to the victims are exhibited at Boston public library
Runners' shoes and other objects that were left at makeshift memorials to the victims are exhibited at Boston public libraryGetty
A cyclist crosses the newly laid official Boston Marathon finish line on Boylston Street
A cyclist crosses the newly laid official Boston Marathon finish line on Boylston StreetReuters

Authorities said two brothers planned and orchestrated the attack and later shot and killed Collier when they attempted to steal his gun. Tamerlan Tsarnaev, 26, died following a shootout with police. Dzhokhar Tsarnaev, 20, was captured and pleaded not guilty to 30 federal charges. He is awaiting trial and faces the possibility of the death penalty.

Prosecutors say Dzhokhar Tsarnaev left a hand-scrawled confession condemning US actions in Muslim countries on the inside of a boat he was found hiding in.

An explosion erupts near the finish line of the Boston marathon in this photo taken by Dan Lampariello on April 15, 2013
An explosion erupts near the finish line of the Boston marathon in this photo taken by Dan Lampariello on April 15, 2013Reuters
A man is loaded into an ambulance after he was injured by one of two bombs that exploded during the 117th Boston Marathon on April 15, 2013
A man is loaded into an ambulance after he was injured by one of two bombs that exploded during the 117th Boston Marathon on April 15, 2013Getty
A woman is comforted by a man after twin explosions at the 117th Boston Marathon on April 15, 2013
A woman is comforted by a man after twin explosions at the 117th Boston Marathon on April 15, 2013Reuters
The four people who were killed in the Boston Marathon bombing and the subsequent manhunt (clockwise from top left): Martin Richard, Sean Collier, Krystle Campbell and Lu Lingzi
The four people who were killed in the Boston Marathon bombing and the subsequent manhunt (clockwise from top left): Martin Richard, Sean Collier, Krystle Campbell and Lu Lingzi
Crime scene investigators work at the site of one of the bombings, the day after the Boston Marathon
Crime scene investigators work at the site of one of the bombings, the day after the Boston MarathonReuters
The two bombers, Dzokhar (L) and Tamerlan Tsarnaev, are pictured during the Boston marathon
The two bombers, Dzokhar (L) and Tamerlan Tsarnaev, are pictured during the Boston marathonReuters
An aerial infrared image shows the outline of Dzhokhar Tsarnaev hiding in a boat in Watertown, Massachusetts, on April 19, 2013
An aerial infrared image shows the outline of Dzhokhar Tsarnaev hiding in a boat in Watertown, Massachusetts, on April 19, 2013Reuters