Trisha Thadani

USA TODAY

BOSTON — Participants and spectators at this year's Boston Marathon will notice a large volume of uniformed police officers once again lining the 26.2-mile route.

Three years after bombings rocked the finish line of the race, security remains greatly enhanced, said David Procopio, a spokesman for the Massachusetts State Police. The course always had a large security presence, but officials increased it exponentially after two homemade pressure-cooker bombs killed three people and injured more than 260 in 2013.

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"There will be a large contingent of plainclothes and investigative officers who will make observations of any suspicious activity, and observe the behavior of members of the public along the marathon route," Procopio said. "Behind the scenes, the public will not feel it, but there will be heavy intelligence as well."

A massive manhunt in the days following the 2013 bombings targeted brothers Dzhokhar and Tamerlan Tsarnaev. A shootout with police killed Tamerlan a few days after the marathon. Police captured Dzkohkar alive several hours later. A jury convicted him for his role in the bombings, and he was sentenced to death.

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Procopio said the safety precautions and police presence this year will be similar to the past two. Drones are banned, and spectators are encouraged not to bring backpacks as they may be subject to search.

The FBI said there is no actionable or credible threat to the marathon, but it will be hyper-vigilant about anything suspicious or anything that could develop into a threat.

The U.S. Department of Energy’s National Nuclear Security Administration has been flying a low-altitude helicopter over the marathon route this week to measure baseline levels of radiation. The department says it’s a normal part of security and emergency preparedness, and citizens should not be alarmed.

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Law enforcement agencies are taking steps to ensure the security presence is not overwhelming, Procopio said.

“We don’t want to create an environment akin to an armed camp or a military base. We don’t want participants or spectators to feel like they are in an environment like that,” he said. "Just enjoy yourselves and leave the worrying to us."

Follow USA TODAY reporter Trisha Thadani on Twitter: @TrishaThadani