BOSTON (AP) — One year after a pair of homemade pressure-cooker bombs killed three people and wounded more than 260 others at the finish line of the Boston Marathon, runners started filtering in Monday morning as the sun rose over the center of Hopkinton, where the race starts.

About 36,000 runners have registered for the race — the second-largest field in its history, many of them coming to show support for the event and the city that was shocked by the attack on its signature sporting event.

"I can't imagine the number of emotions that are going to be there," said Katie O'Donnell, who was running the marathon last year and made it 25½ miles before she was stopped less than a mile from the finish line when the twin bombs exploded. "I think I'm going to start crying at the starting line and I'm not sure I'll stop until I cross the finish line."

The most obvious change for the 118th edition of the world's oldest annual marathon was the heavy security presence. State and local police officers were everywhere, even on the rooftops of some buildings.

A bus dropping off runners had the words "Boston Strong" on the electronic sign at the front that usually posts the bus's destination. A banner posted on a commercial building in Hopkinton read: "You are Boston Strong. You Earned This."

Spectators coming to the start line had to pass through police checkpoints.

"There'll be considerably more police presence," Massachusetts Gov. Deval Patrick said Sunday on CBS' "Face the Nation." ''But we also don't want to have it, you know, kind of a race through a militarized zone. So it's about striking a balance, and I think we have struck that balance."

Runners attending the event will have to use clear plastic bags for their belongings, and fans hoping to watch near the finish line are encouraged to leave strollers and backpacks behind. More than 100 cameras have been installed along the route in Boston, and 50 or so "observation points" will be set up around the finish line "to monitor the crowd," the Boston Athletic Association said.

Patrick said there have been no specific threats against the race or the city for the Massachusetts holiday of Patriots' Day.

"We're not taking that as a sign to sort of stand down," he said. "We're very prepared, and we're assuring people as much as we can that it'll be a fun day and a safe one."

Race organizers expanded the field from its recent cap of 27,000 to 36,000 make room for more than 5,000 runners who were still on the course at the time of the explosions, for friends and relatives of the victims and for those who made the case that they were "profoundly impacted" by the attack.

Lelisa Desisa of Ethiopia and Kenya's Rita Jeptoo, who crossed the finish line on Boylston Street about three hours before the explosions, will return to defend their championships. Desisa returned to Boston last fall to donate his first-place medal to the city as a gesture of support.

Jeptoo, who also won the race in 2006, said she is hoping for a third victory — and one she can enjoy.

"It was very difficult to be happy. People were injured and children died," she said of last year's marathon. "If I'm going to win again, I hope I can be happier and to show people, like I was supposed to last year."

Authorities say two ethnic Chechen brothers who lived in the former Soviet republic of Kyrgyzstan and the Dagestan region of Russia planned and orchestrated the marathon bombings on April 15, 2013.

Tamerlan Tsarnaev, 26, died following a shootout with police days after the bombings. Dzhokhar Tsarnaev, 20, has pleaded not guilty to federal charges and is awaiting a trial in which he faces a possible death sentence. Prosecutors say the brothers also killed MIT police Officer Sean Collier days after the bombings in an attempt to steal his gun.

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Follow Jimmy Golen on Twitter at: http://www.twitter.com/jgolen

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Associated Press writer Bob Salsberg in Hopkinton contributed to this report.