Boston Marathon bomber suspect Dzhokhar Tsarnaev targeted men, women and children at the marathon because he wanted to terrorise the US, a federal prosecutor has said.

The jury will begin deliberations on Tuesday, after the prosecution and defence made their closing arguments on Monday.

Tsarnaev is charged with conspiring with his older brother, Tamerlan, to bomb the marathon in April 2013.

Three people were killed and more than 260 were injured when two pressure-cooker bombs exploded near the finish line. Dzhokhar could face the death penalty if convicted. Tamerlan was killed in a gun battle with police days after the bombing.

"He chose a day when there would be civilians on the sidewalks. He and his brother targeted those civilians, men, woman and children, because he wanted to make a point. He wanted to terrorise this country," Assistant US Attorney Aloke Chakravarty said in his closing remarks on Monday.

"He wanted to punish America for what it was doing to his people. So that's what he did."

Chakravarty showed the jury a photo of Tsarnaev standing just feet behind 8-year-old victim Martin Richard, his family, and other children who were standing on a metal barricade to watch the runners cross the finish line. He said Tsarnaev placed his bomb right there, the second bomb that would explode that day.

"These children weren't innocent to him. They were American ... Of all the places that he could have placed the bomb, he placed it right here."

Chakravarty also played a gruesome video of the aftermath of the first bombing, which showed gravely injured people scattered on the pavement and huge pools of blood. As first responders and volunteers try to help the injured, screams and moans punctuate the video, along with shouts of "Help!"

Defence frames brothers' roles

Defence lawyer Judy Clarke, who has saved some of America's most notorious convicts from the death penalty, said Tsarnaev deserved to be condemned but that the attacks would never have happened without Tamerlan.

Her team portrayed the older Tamerlan - who was killed by police while on the run after the attacks - as the architect of the bombings, arguing that his younger sibling had fallen helplessly under his influence.

Tamerlan built the bombs, murdered police officer Sean Collier, downloaded the bomb-making instructions, brought the bomb materials, the backpacks and his finger prints were all over the evidence, she said.

"Let's be honest about what the evidence actually shows. We're not asking you to excuse the conduct but lets look at he varying roles," Clarke said.

"He was an adolescent drawn into the passion and belief of his older brother and still living a teenage life. He was flunking out of school and making up lame excuses about why he was failing," she said.

Source: Agencies