MIT police Sergeant Dave O’Connor stood by in uniform watching as the air horn blew in the misty gray light early Sunday morning and nearly 9,000 runners bounded across the starting line of the ninth Run to Remember.
The half-marathon and 5-mile races, dedicated to law enforcement officers killed in the line of duty, drew police officers, military personnel, and civilians to honor the first responders to the Boston Marathon bombings and MIT police Officer Sean A. Collier, shot and killed in his squad car the night of April 18, allegedly by the bombing suspects.
“These events are what’s keeping us on our feet right now,” O’Connor said. “Since the night of Sean’s death, the Massachusetts community has taken us into its arms. . . . The Massachusetts community, the whole US community, have no idea what events like this do to keep us together.”
Collier had told friends he wanted to register for the race, which started at 7 a.m. outside the Seaport World Trade Center and circled Downtown Boston, then ran across the Longfellow Bridge and down Memorial Drive in Cambridge before looping back.
For the first time, registration for the race exceeded its 10,000 capacity, with 10,800 runners signing up and an estimated 8,800 making the run, according to race director Steve Balfour.
Balfour, whose father was among the founders of a memorial race for fallen police officers in Melrose and Wakefield 13 years ago, said organizers expected to reach capacity, but not as quickly as they did. Registration closed in April for the run, which benefits the Boston Police Runners Club children’s programs.
Usually, about 200 people register weekly as the race nears, Balfour said. This year, about 3,000 signed up in the week after the Boston Marathon.
“An hour after the bombing in the Marathon, registration started clicking,” Balfour said.
More runners signed up after Collier was killed and his friend, MBTA police Officer Richard “Dic” Donohue, was badly wounded in the shoot-out in Watertown between police and the bombing suspects. Donohue is now recovering at Spaulding Rehabilitation Center.
Collier and his friend Chrissy Natoli were supposed to be running the race together Sunday. Collier had approached Natoli about two months ago and proposed they run the half-marathon together.
“I was honored he asked me to do the race with him,” said Natoli. She knew that at the time it was a personal thing for Collier.
“Now it’s an extremely personal thing for me,” she said.
“It was definitely very emotional,” said Natoli about running the race Sunday without her friend.
“I had tears in my eyes as I got closer and closer to the finish,” said Natoli. “I knew I was supposed to be there with him, and I knew his spirit and his energy were pushing me to the finish line.”
As the morning progressed, runners, including the current Massachusetts Transit Police Academy class, streamed across the finish line. Together, the class matched one another’s strides and ended the half-marathon run to applause from the surrounding crowd of both fellow runners and supporters.
The class entered the cool-down area, where volunteers offered water and food and chanted in unison “How strong? Collier strong!” Collier’s badge number 179 was displayed proudly on each runner’s back.
All participants were given a race bib with the fallen officer’s name and badge number on it before the run began.
The class decided to run the half-marathon in a tribute to Collier and Donohue, both graduates of the academy.
Law enforcement from all over the country participated in the run, including officers from New York and Chicago.
New York Police Officer Frank Bonilla, 39, said he was part of a group of officers who came to run and support the cause.
“When they asked me to run it, I couldn’t say no,” said Bonilla, who has been on the NYPD for 14 years. “Even guys who aren’t runners came up to show support for Boston, MIT, and Watertown.”
In Afghanistan, Monique Hassan, a US Army general surgeon, stationed in Khost, helped organize her own version of the race in solidarity with Boston. The race in Afghanistan had more than 60 participants for the 13.1-mile run.
The runners started at 5 a.m. because, she said in an e-mail, temperatures are “over 100 degrees on most days here.”
Hassan said she organized the event, and also ran the race.
“Everyone had a great time; it was not only team building and morale boosting but a moment of reflection in memory of those who have lost their lives.”
In Boston, security was tight around the race. Volunteers directed the flow of runners around the Seaport World Trade Center before and after the race, making sure only runners, volunteers, and a few supporters entered. Security personnel checked the bags of people entering the area around the starting and finish lines, and runners were told to keep their belongings in clear plastic bags.
Police Commissioner Edward F. Davis, who briefly spoke to runners before the race, said he is working to make heightened security the norm at large events.
“This is usually a very low-key security event,” Davis said, “but this year’s security is increased.”Globe Correspondent Peter DeMarco contributed to this report. Gal Tziperman Lotan can be reached at email@example.com. Derek J. Anderson can be reached at firstname.lastname@example.org.