BOSTON >> Extraordinary security measures are being taken during the federal death penalty trial of accused Boston Marathon bomber Dzhokhar Tsarnaev, perhaps the most scrutinized U.S. terror case since the Oklahoma City bombing.

White SUVs from Homeland Security line up bumper-to-bumper in front of Boston’s federal courthouse while others periodically circle the block. Boston police officers patrol the perimeter on foot, and a dark special operations van is stationed near the entrance. In the harbor nearby, armed U.S. Coast Guard boats ply the waters, and inside the court building officers with dogs roam the hallways.

The U.S. Marshals Service, which oversees courthouse security, declined to comment on measures for the trial and Boston police spokesman Michael McCarthy said his department is not aware of any credible threats. McCarthy said the department is simply providing support to federal authorities, although he declined to say how many city officers or which units have been assigned.

But there’s even more going on behind the scenes, according to Rick Avery, northeast region president for Securitas, a private security company not involved in security for the trial.

Bomb squads, snipers, undercover officers and enhanced surveillance operations are just some of the measures used to secure high-profile terrorism trials, Avery said. Tsarnaev’s trial, which began this week with jury selection and is expected to last three to four months, is no exception, he said.

“Federal courthouses have a very high level of security to begin with, so what you’re doing is basically extending the security barrier beyond the courthouse doors,” Avery said. “The possibility of something happening exists every day, so I’d imagine they’re being a little more cautious with this.”

Tsarnaev, 21, faces the death penalty if convicted for his role in the twin bombings at the marathon finish line in April 2013, which killed three people and wounded more than 260 others. Tsarnaev also is charged in the slaying of an MIT police officer in the days after the bombing.

Boston’s federal courthouse is used to heightened security, most recently in 2013, when notorious gangster James “Whitey” Bulger was tried, convicted and sentenced there.

Law enforcement officials will be keeping a watchful eye on the demonstrators and onlookers the proceedings periodically have drawn, as well as the hundreds of prospective jurors who have been filing in and out of the courthouse complex.

They’ll likely also be keeping tabs on social media, where Tsarnaev’s supporters and bombing conspiracy theorists have been active.

The heightened awareness extends to nearby businesses along the rapidly developing waterfront.

At Vertex Pharmaceuticals, located next to the courthouse, employees said the company notified workers to brace for parking disruptions and other hassles.

Security guards posted at the building entrance, though, declined to comment about any additional safety measures being taken.

“This is not new to the city or the federal courthouse,” Avery said. “They are more than capable of securing these things. Between the federal, city, (Massachusetts Port Authority) and state police, they’ve got this covered.”