In just a dozen seconds, two pressure-cooker bombs exploded at the finish line area of the Boston Marathon last year, creating a tailspin that lasted for days. On Friday, the police officer killed during the manhunt for the bombers was memorialized as the region continued to mark the anniversary of the tragic events.
Three people died in the explosions and more than 260 people were injured.
The fourth death took place a year ago Friday when MIT Police Officer Sean Collier was shot, allegedly by the fleeing suspects, Tamerlan and Dzhokhar Tsarnaev.
Tamerlan died after a later shootout with police in Watertown, Mass. Dzhokhar was apprehended on the night of April 19, 2013 and is awaiting trial on charges that could bring the death penalty if he is convicted.
On Friday, the MIT community mourned Collier's death at a ceremony at the school in Cambridge. With Collier's family attending, Sara E. Ferry, a friend and graduate student, described his death as "moment of extreme evil."
"Sean embodied the spirit of MIT and the students," said Ferry, according to local media reports. "He was always learning. … We are so grateful that he was part of lives at MIT. … When Sean left us, love rushed in. … Love will be Sean's legacy at MIT."
U.S. Sens. Edward Markey and Elizabeth Warren, both Democrats from Massachusetts, also praised Collier. Cambridge Mayor David P. Maher said the intersection near where Collier was sitting in his police cruiser when he was shot would be named Sean Collier Square as a memorial.
Friday morning's ceremonies was also a fundraiser for the Sean A. Collier Memorial Fund, which has raised more than $500,000 to pay for scholarships at MIT and the Massachusetts Police Academy.
Team Collier Strong, a group of about 25 friends and relatives, will be running in Monday's Boston Marathon to raise scholarship money for the fund.
The bombs went off on April 15, 2013 and the Boston region has been commemorating events with moments of silence, prayers and ceremonies this week as the area works through the healing process. Those killed in the blasts -- Krystle Campbell, 29, Lu Lingzi, 23, and Martin Richard, 8 -- have all been remembered and mourned.
Collier was the fifth of six children. He studied criminal justice at Salem State University, working for a time as a civilian at the Somerville Police Department. He was a fan of the Boston Celtics, taught young people to box and helped out at a homeless shelter. When the MIT Outing Club headed to Newfoundland for a weekend of hiking, Collier joined them.
Collier's sister, Nicole Lynch, told reporters this week that the family was relieved when her brother was hired for a relatively quiet police post at MIT.
"Then he called me after his first week and said, 'I made my first traffic stop and they pulled a knife on me,' " she told the Associated Press. "I remember thinking, 'Oh my goodness, maybe this is not as safe as I thought.' "
Tucked within the solemn moments this week has also been the occasional moment of joy.
On Thursday night, Marc Fucarile and Jen Regan finally married. They had been planning their ceremony last year, but the bombing cost Fucarile his leg and the nuptials were put on hold.
During his recuperation, Regan entered a contest offering a free wedding to a couple who was affected by the bombings. She wrote an essay and won.
The wedding took place Thursday night at the EMC Club at Fenway Park, home of the Boston Red Sox.
The wedding's colors were blue and yellow -- to match the logo of Boston Strong, the city's mantra.