BOSTON - Even as police prepare for a massive presence at Boston's first marathon since the 2013 bombing attack that killed three people and injured 264, officials acknowledge the sheer scale of the event poses inevitable security risks.
More than 3,500 officers will be stationed along the 26.2 mile (42.2 km) course starting in suburban Hopkinton, Massachusetts, and ending among throngs of spectators at the bars and restaurants of Boylston Street, where two homemade pressure-cooker bombs ripped through the crowd last year.
While officials said they are not aware of any specific threat to the 118th Boston Marathon, one of the world's most prestigious races, they face a challenge of increasing security without taking a stance that is so aggressive it drives spectators away, security experts said.
"The police have to walk a delicate line between trying to convey to people that they are safe and not sending the message that, because of the militarized presence, they have something to fear," said Tom Nolan, a former Boston Police Department official who now serves as chairman of the criminal justice department at the State University of New York at Plattsburgh.
"The public may not necessarily be reassured about their safety when they see police officers with machine guns and military uniforms and dogs," Nolan said.
The race, on April 21 this year, is held on the state holiday of Patriots' Day, when schools as well as some businesses are closed, and tens of thousands of spectators typically clog the finish line area. It was there that ethnic Chechen brothers Dzhokhar and Tamerlan Tsarnaev placed the bombs they carried in black backpacks last year.
Knapsacks and large bags will be banned at the finish line and police are warning fans to expect checkpoints and inspections as they approach the course. "In this world, you never eliminate risk. You never bring it down to zero. But we are working very hard at reducing the risk," State Police Colonel Timothy Alben told reporters.
Runners also face new restrictions, including a ban on bags at the starting line. That is a concern for athletes who in years past counted on bringing clothing to keep themselves warm while waiting for the race to start.
Weather conditions in Boston are highly variable in mid-April: While last year's race saw near-ideal temperatures of 65 degrees Fahrenheit (18 Celsius), runners in 2007 waited in wind and driving rain for the chilly 47 F (8 C) start.